X-diff-cover

* Some tweaks to the readme
* Changes to how flake8 is parsed allowing diff_quality to support error codes that dont conform to the suggested 3 letter 3 digit form
* Adds option to show snippets in the console report to help provide context for violations
* Some tests migrated from unit test's class based approach to pytests functional approach

All of these are due to kasium Thanks for all you have done to this point!

* Adds 'num_changed_lines' to json report. Thanks kasium https://github.com/Bachmann1234/diff_cover/issues/170

* Adds 'quiet mode' which will only print errors and failures. Flag -q thanks kasium https://github.com/Bachmann1234/diff_cover/issues/160
* Several internal improvement to tools and configs. Thanks kasium !

* Fixes a bug where clover reports were not counting conditionals (Thanks for ZSmallX providing a detailed report that made fixing this easy) (https://github.com/Bachmann1234/diff_cover/issues/190)
* Switch to github actions for CI as I ran out of free credits for travis and this job does not pay
* Drop 'official' support for pypy3. I don't really have any reason to think pypy wont work for this project and I wanted to simplify my ci builds.

* Bug fix to in include's functionality around absolute vs reletive paths (Thanks Kasium https://github.com/Bachmann1234/diff_cover/pull/187)
* Some pylint fixes (Thanks Kasium https://github.com/Bachmann1234/diff_cover/pull/186)

* Add the --includes option for diff-quality (Thanks kasium https://github.com/Bachmann1234/diff_cover/pull/184)