checkbashisms: add "lint" option

This option makes checkbashisms output gcc-style warnings, a common way of integrating linters into editors. other shell-related utilities (like shellcheck), have the ability to output like this.

Currently the column defaults to column 1, since checkbashisms does not yet point out the column that the bashism occurs yet, only the line.

I wasn't sure what the option should be called exactly; shellcheck does it with an -f gcc option, and while a -f/--format argument would be nice, I don't think something this small warrants adding all that functionality.

Additionally, if I'm understanding the CI output correctly, it says that this code isn't conforming to the perltidy rules. I've checked it myself and it seems correct though...?