config.py

--max-report-size:
  Old: in --html-dir this limited only the parent page
  New: in --html-dir this applies across all pages

--max-diff-block-lines:
  Old: in --html-dir 4 * this number applied across all pages (for a given diff block)
  New: in --html-dir this applies across all pages (for a given diff block)

--max-page-size:
  New flag
  Applies to the sole --html page, or the top-level --html-dir page

--max-report-child-size
  Renamed to
--max-page-size-child:
  No behavioural changes

--max-diff-block-lines-parent
  Renamed to
--max-page-diff-block-lines:
  Old: Only applied to the top-level --html-dir page
  New: Applies to the sole --html page, or the top-level --html-dir page

The reasoning behind these changes is that it's unlikely someone would want to
generate a 500MB single html page, but they might in theory generate a 500MB html
directory split up into several 200KB pages, plus a single 200KB html page as
a summary. The new semantics for these flags allows both to be generated in one
run using the same set of flags.