v2.13.0

• Fixed importing of modules that have the same name as the file that is importing.
  astroid will now correctly handle an import math statement in a file called math.py
  by relying on the import system.

  Refs pylint-dev/pylint#5151

• Create ContextManagerModel and let GeneratorModel inherit from it.

  Refs pylint-dev/pylint#2567

• Added a regex brain.

  Refs pylint-dev/pylint#1911

• Support "is None" constraints from if statements during inference.

  Refs #791
  Refs pylint-dev/pylint#157
  Refs pylint-dev/pylint#1472
  Refs pylint-dev/pylint#2016
  Refs pylint-dev/pylint#2631
  Refs pylint-dev/pylint#2880