[Typing-sig] pyanalyze, a newly public type checker

I just open sourced pyanalyze (https://github.com/quora/pyanalyze), a static analysis tool and type checker. The announcement post is in https://www.quora.com/q/quoraengineering/Static-analysis-at-Quora-and-pyanal.... Pyanalyze was initially written as a static analysis tool specifically for checking some common patterns in our codebase at Quora, but we extended it to perform a subset of PEP 484 type checking. I hope the tool will be useful to others as well!