Other fixes to packaging

Summary:
Basically make sure that license information is properly preserved in metadata, source and built distributions.

Also, start having a .gitignore with common stuff.

Reviewed By: adamlerer

Differential Revision: D15166521

fbshipit-source-id: 3b64e208829f3983fc2ad589c6608b584e6b40ac

Initial commit

fbshipit-source-id: 40ae73746a329c8f6b8df3af34b004cc946e42d9