Sync to upstream github:
- Better approach to testing.
- Fix and greatly expand stubs for sqlalchemy.
- Expand the sqlalchemy stubs related to the Column model.
- Type Check webbrowser py3 module
- Add missing exec*, EX_* stubs for python 2 and fix py3 types.
- Add py2 webbrowser type checking
- Fix urlunparse stubs for 2.7 to correctly support a list/iterator argument
- Improvements to builtins min/max
- Try using "pip install -U ..." to install mypy
- Add missing definition of compile() for 2.7.
- Add abc.abstractproperty (Python 3)
- Fix incorrect sys.exit() type.
- Additional type information for asyncio