feat(fonts) - Configuration of Font Directory

resolves #45

* Introduce a standard gem configuration interface that allows
  users to set an alternate font directory as follows:

```ruby
Prawn::Icon.configure do |config|
  config.font_directory = '/foo/bar'
end
```

* Formally deprecate the `FONTDIR` and `SHIMS` constants and replace
  with memoized class variables. We're only keeping them around so
  as to not release a breaking change.
* Fix a bug with directory pathing in some environments because the
  path was built assuming consistent namespacing. We now use
  `Gem::Specification#full_gem_path` to handle the inconsistencies.
* Disable the rubocop `Layout/MultilineMethodCallIndentation` check
  as it adds more whitespace than I prefer.

feat(fontawesome): Update FontAwesome to 5.15.0

* Update the fontawesome fonts and legend files from
  version 5.11.2 to 5.15.1.
* See FontAwesome's [upgrade guide](https://github.com/FortAwesome/Font-Awesome/blob/master/UPGRADING.md) for more details.

fix(inline): Inline Icon Page Wrapping

* Previously inline formatted icons would not correctly start a
  new page when necessary, so the formatted text box would render
  at a cursor position that made it invisible.
* Add a new test case for the bug outlined in #49.
* Adjust `#inline_icon` to directly call Prawn's `#formatted_text`
  method with the transformed inline formatted string.
* The previous implementation of `#inline_icon` went to great
  lengths to position the formatted text box without rendering to
  the document, but Prawn's formatted text box wrapping logic may
  require multiple `Prawn::Text::Formatted::Box` instances (around
  page breaks).
* Due to this change `#inline_icon` calls now return `nil` and
  content is rendered immediately to the document.
* This change also means that `#icon` calls will return `nil`
  when using the `inline_format: true` parameter.
* Add a `#formatted_icon_box` method that retains the previous
  inline icon behaviour.
* Allow `#formatted_icon_box` to accept the `:at`, `:x` and `:y`
  absolute positioning parameters (Thanks @navisnspm!).
* Transition to `Pdf::Inspector` to make positioning decisions
  in specs. This is a more comprehensive test expectation.
* Change the deprecation message for the FontAwesome 4
  shim to include a future 4.X version as the compatibility
  layer will be maintained for at least another major version.
* Update major version to 3.0.0 as the return values have
  changed in the public API `#icon` and `#inline_icon` methods.

TravisCI -> GitHub Actions

* Setup github actions to execute the test suite in a build
  matrix using ruby 2.6.X and 2.7.X along with various versions
  of prawn.
* Remove the `.travis.yml` file - we'll no longer be using
  travis for CI.

Version 2.5.0

* Update FontAwesome from `5.8.2` to `5.11.2`.
* See FontAwesome's [upgrade guide](https://github.com/FortAwesome/Font-Awesome/blob/master/UPGRADING.md) for more details.
* Fix rspec proc syntax for expectations in specs after a version bump.
* Exclude prawn master from the build for jruby 9.1.13.0 as it
  is failing in CI.

Release 2.4.0

* Update FontAwesome from `5.4.0` to `5.8.2`.
* See FontAwesome's [upgrade guide](https://github.com/FortAwesome/Font-Awesome/blob/master/UPGRADING.md) for more details.
* Update the Payment Icon URL to https://paymentfont.com.

FontAwesome 5.4.0

* Update fontawesome from version `5.0.13` to `5.4.0`.
* Update font licences to latest version from upstream.
* Release gem version 2.3.0.

Update FontAwesome to 5.0.13

* Move out shim configuration into a `.yml` file located
  inside the `data/fonts/fa4/shims.yml` file.
* Update FontAwesome TTF files and legend files from 5.0.8
  to 5.0.13.
* Add additional compatibility shims that were missing for
  some icons from FontAwesome 4. This version release is
  now fully backwards-compatible with all icon specifiers
  present in FontAwesome 4 (via version `1.4.0` of this gem).
* Fix a bug in the FontAwesome converter tool by properly
  requiring `fileutils` before execution.
* Remove ruby 2.2.X from the travis build as `prawn` master
  has removed compatibility with this version of Ruby
  (see: https://github.com/prawnpdf/prawn/pull/1060).
* Bump the version of jruby when on the travis builds to
  match prawn master.
* Remove `rbx` from the travis builds. They always error
  and require more time to build.

2.1.0 - FontAwesome 4 Shim

* Add a compatibilty class that includes FontAwesome 4
  shim data from the FontAwesome metadata.
* Effectively rewrite all instances of `fa-*` to their
  appropriate FontAwesome 5 font family.
* Perform the icon key rewrite at the higest scope possible
  in `Prawn::Icon::Interface` to retain backwards compatibility.
* Add a deprecation warning whenever `fa-*` references
  are encountered.
* Disable the `Layout/IndentHeredoc` rubocop rule to not
  have to include further dependencies for heredoc
  indentation.
* Bump version to 2.1.0.

FontAwesome 5

* Update `Prawn::Icon` version to `2.0.0`. This will be a breaking
  release due to significant changes in FontAwesome (icons are now
  namespaced by style).
* Completely remove GitHub Octicons - this font is no longer released
  as a `.ttf` file (https://github.com/blog/2112-delivering-octicons-with-svg).
* Create the `fab`, `far` and `fas` specifiers and legends for
  FontAweomse brands, regular and solid styles.
* Write a helper script to accept the FontAwesome icon metadata
  YAML file (https://github.com/FortAwesome/Font-Awesome/blob/31281606f5205b0191c17c3b4d2d56e1ddbb2dc6/advanced-options/metadata/icons.yml) and create the correct legend files.
* Completely remove the `fa-*` namespace. All FontAwesome icons are
  now under `fab-*`, `far-*` or `fas-*` namespaces.
* Update the README and CHANGELOG to reflect breaking changes.
* Require `prawn/icon/version` by default.

Version 1.4.0

- Update dependency gems to latest version.
- Fix `rubocop` config to show cop names as well as increase the ABC complexity slightly.
- Add internal tooling to assist with the SCSS => YAML mappings of FontAwesome and PaymentFont.
- Update FontAwesome to `v4.7.0` from `v4.6.3`. See [changelog](http://fontawesome.io/icons#new).
- Update PaymentFont to `v1.2.5` from `v1.1.2`. See [icons](https://paymentfont.com/#icons).
- Update Octicons from to `v4.4.0` from `v3.1.0`. NOTE: As Octicons have moved from font-based icons to SVG after this version, this will be the final octicon version in `prawn/icon`. See the [wiki](https://github.com/blog/2112-delivering-octicons-with-svg).
- Fix rubocop warnings for whitespace.
- Remove ruby `2.1.0` from travis, test against `2.4.1` instead.

Interface - v1.3.0

* Break out Prawn::Icon::Interface into its own file [#27].
* Add simplecov as a development dependency.
* Update rubocop to 0.44.1.
* Bump version to 1.3.0.

Prawn::Icon::Base [#27]

- Bump version to v1.2.0.
- Update FontAwesome from v4.5.0 to v4.6.3.
- Refactor spec files to remove duplication using `let` blocks.
- Break internal dependencies to `Prawn::Icon::Base` to allow selective code requires.
  (see issue #27).
- Introduce `Prawn::Icon::Errors` to contain internal exception classes.
- `Prawn::Icon::FONTDIR` is now an alias to `Prawn::Icon::Base::FONTDIR` for compatibilty.
- Add basic spec files for `Prawn::Icon::Base` and separate exception classes.
- Minor backwards-compatible code refactor of `Prawn::Icon::FontData` for readability.
- Point legend rake task code to `Prawn::Icon::Base::FONTDIR`.
- Add a spec to test inline_icon with final_gap: false to achieve 100% coverage.

Fix Inline Icon Render Position

* Remove extra 2.1.* ruby versions from Travis.
* Update Travis config to match (almost) that of Prawn's.
* Let Travis test against Prawn 2.1.0.
* Remove unused mocha and simplecov development dependency
  from gemspec.

* Break out line gap and leading calculation into its own private
  method for Text::Formatted::Box's that are used for icons.
* Add spec to test for the correct inline icon render position (#24).
* Update version to 1.1.1.
* Update Changelog.

* Modify `inline_icon` method to render at the cursor position
  and perform a dry_run render of the Text::Formatted::Box to
  determine the height of the box.
* The y position is then moved down the height of the text box
  (with line gap and leading if applicable).

New address, fix spaces and the renamed LGPL

This is an exact copy of http://www.gnu.org/licenses/old-licenses/gpl-2.0.txt

Version 1.1.0

* upgrade font-awesome to v4.5.0
* refactor specs and update development dependencies
* update changelog and bump version
* disable a few rubocop checks
* fix unnecessary spacing in parser.rb
* require a new version of bundler on travis before install

Simplify code using Ruby's tap method

update octicons to v3.1.0

Update FontAwesome to 4.4.0.