-----
- ``--disable`` and ``--enable`` now support the special string "all" to refer to
all codes. Explicit enables and disables are given higher precedence than "all".
- Add ``E110`` for catching the return of a known-``None`` variable immediately
after testing it (prefer to return ``None``, not the variable name)
- ``--disable`` and ``--disable`` now support categories, as in ``--disable W``
to disable all warnings.
- The ``E101``, ``E102``, and ``E103`` codes have each been downgraded to warnings
(``W`` category) but are still enabled by default
- The matching AST checker now considers the triviality and proximity of
matching AST nodes. By default, only the check for non-trivial adjacent
branches is enabled.
- Add ``W201``, ``W202``, and ``W203`` to describe the disabled checks
- Triviality is defined as a heuristic which captures simple expressions and
statements (e.g. ``return None`` is a trivial statement)
- Add support for ``--enable`` to turn on disabled codes