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