Fixed
* Fix type annotations for `convertFile` - it accepts only bytes-based buffers.
Also remove legacy checks from Python 2 (1400)
* Remove legacy import needed only in Python 2 (1403)
* Fix typo that left the attribute `AdmonitionProcessor.content_indent` unset
(1404)
* Fix edge-case crash in `InlineProcessor` with `AtomicString` (1406).
* Fix edge-case crash in `codehilite` with an empty `code` tag (1405).
* Improve and expand type annotations in the code base (1401).
* Fix handling of bogus comments (1425).