Per the urllib.parse documentation, username, password, hostname,
and port will be set to None if not set in the parsed URL. The
same is true for urlparse in Python 2 according to its documentation.
Also adds the bare minimum of stubs for
cryptography.hazmat.primitives.asymmetric to define the types
referenced here. (cryptography is a full project in its own right,
with lots of types and internal references.)
This tries to use bytes in places where the module documentation
emphasized that this was opaque bytes and str for arguments and
return values that the module seemd to be treating as regular Python
strings, even though this distinction is not horribly meaningful for
Python 2.
