Prep for 1.20.0

[avylove]

Preparation for releasing 1.20.0

• Update version and history
• Add fix for get_keyboard_codes() can throw a RuntimeError if a global variable is created while it is running #248
• Add fixes for Pylint
• Move to 3.11 for base python in testing
• Add 3.10 and 3.11 to package classifiers

[codecov]

Codecov Report

Base: 95.38% // Head: 95.38% // No change to project coverage 👍

Coverage data is based on head (9507d44) compared to base (faf10af).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #250   +/-   ##
=======================================
  Coverage   95.38%   95.38%           
=======================================
  Files           9        9           
  Lines        1018     1018           
  Branches      215      215           
=======================================
  Hits          971      971           
  Misses         43       43           
  Partials        4        4           

Impacted Files	Coverage Δ
blessed/__init__.py	77.77% <100.00%> (ø)
blessed/keyboard.py	100.00% <100.00%> (ø)
blessed/terminal.py	98.27% <100.00%> (ø)

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