This updates all the object creation functions and utility context

managers in TestCase to provide type hints. This helps to write better

type-safe unit tests, and resolves a lot of problems that currently

exist when passing in values that default to None or accept multiple

value types.
In the process, documentation has been updated to meet current standards.
There are a couple of fixes in here. For instance, create_visit()

ignored the timestamp field and didn't normalize user correctly, and

http_request() passed in bad empty arguments when constructing a

ResolverMatch. These have been addressed.

All unit tests pass.