Modify Table repr

[dantownsend]

By default, the repr for a Python class type is something like:

>>> repr(MyTable)
<class 'my_app.tables.MyTable'>

It's a very common pattern in Piccolo and its sister libraries to have Table class types as default values:

# `SessionsBase` is a `Table` subclass:
def session_auth(
    session_table: t.Type[SessionsBase] = SessionsBase
):
    ...

This looks terrible in Sphinx's autodoc output, as Python's default repr contains angled brackets, which breaks the HTML output.

So we just need to output the name instead. The user can still easily find which module a Table subclass belongs to by using MyTable.__module__.