Summary:
This was motivated by t7518166. checkCpp crashes on db_test.cc because the file is too big :(
Couple of changes:
* Added clang-format linter. Now we can catch all code that is not formatted correctly.
* Added Howtoeven in our list of linters
* Replaced cpplint with flint
* Removed checkCpp lint. Nobody ownes it and it doesn't work on db_test.cc
Test Plan: Made a random lint error and `arc lint`. Saw an error.
Reviewers: yhchiang, kradhakrishnan, anthony, sdong
Reviewed By: sdong
Subscribers: dhruba, leveldb
Differential Revision: https://reviews.facebook.net/D41949
