Dropped Python3.6 support

Some relatively minor fixes and improvements. The most significant update (and the reason for the major version bump) is that Rich has dropped Python3.6 support.

If you are a Python3.6 user and can't upgrade for whatever reason, pin to version 12.6.0.

[13.0.0] - 2022-12-30

Fixed

• Reversed pre and code tags in base HTML format #2642
• Improved detection of attrs library, that isn't confused by the presence of the attr library.
• Fixed issue with locals_max_length parameter not being respected in Traceback #2649
• Handling of broken fileno made more robust. Fixes #2645
• Fixed missing fileno on FileProxy

Changed

• Bumped minimum Python version to 3.7 #2567
• Pretty-printing of "tagged" __repr__ results is now greedy when matching tags #2565
• progress.track now supports deriving total from __length_hint__

Added

• Add type annotation for key_separator of pretty.Node #2625