Possible naming improvements

I was a bit surprised when approaching the package by the complexity of the naming.

What surprised me :
1. the tool is named pyannotate but you must import pyannotate_runtime to use it
2. collect_types.init_types_collection() ? Does the name really need to be that long ? Do we really need to explicitly init by the way ? Why not initialize on first resume() ?
3. dump_stats() is ok but dump() is good too

Suggestions :
- allow to import directly from pyannotate
- 3 functions only : start(), stop(), dump()
- initialize on first start() or rename init_types_collection() to init()

By the way, I am looking into contributing to pyannotate.