To-do
-----

- PEP8 checking

- allow unicode in .txt files with BOM, or `coding: UTF-8` header

- do a `check_ignore_*` for every kind of checker separately

- Add some more files to run the checks on. e.g. to refline.srccheck.testing

- Add some filtering for CSS validation for known-good but cssutils unsupported
  properties and stuff (e.g. -moz-*)