* Improve types for CalledProcessError
This adds union types in the constructor to account for parameters that
might be either byte strings or unicode strings. At the same time, this
*removes* specific types from the user-accessible fields, to avoid the
need for users to at every use site specify which types their particular
instance was instantiated with.
* remove 'moral' comments; add List import; change 'str' to 'Text'
* import Text
* List -> Sequence; reinsert 'moral' comments
* Regularize string types everywhere
This defines _TXT and _CMD aliases, and uses them everywhere applicable.
Also brings the _FILE alias to python3.
* fix typo; possibly fix indentation
* remove trailing comma, which caused problems in python 2 tests
* fix py2 outputs to be bytes; tweak descriptive comments; remove one AnyStr
* Add `None` to type union for `subprocess.Popen.communicate` stub's `input` parameter.
* subprocess.communicate `input` annotated as `Optional[AnyStr]` for both 2.7 and 3.x; `timeout` as `Optional[float]`.
