closes #983, #1045, #1085 (match)

Opened after @char101 said it was okay to open a PR for this. Many thanks to them for adding match statement support for yapf!

lib2to3 is no longer maintained, this forks lib2to3 and includes some modifications backported from black's blib2to3.

I've looked into modifying yapf to work directly with blib2to3 instead of forking it but this work is in-progress and may not be possible. In addition it holds the risk that the black team does not consider blib2to3 as meant for other projects to consume.

I personally feel that a better long term approach would be for the black and yapf projects to externalize blib2to3 as a separate package that each project depends on rather than having each maintain their own fork.