* Rewrite lint.sh as check_lint.py
This makes several beneficial changes:
* Runs in parallel: lint all now takes 5.5 seconds, down from 25.
* Supports linting specific files, passed on the command-line.
* Defaults to linting files changed since master, pass --all to lint
everything.
* Infers header language based on related files.
* Lays the groundwork for linting more than just C++.
* Adds support for linting python.
* Fix lint errors
* Use check_lint.py in check.sh
* Remove lint.sh
* Python lint configuration
* Enable python linting in travis
