Update to version 2.3.1

Changes between 2.2.0 and 2.3.1:

• Add three new built-in styles, numpy_with_merge, google_with_merge, and numpy_napoleon_with_merge, which permit users to concatenate the respective sections of a parent's and child's docstrings.
• Added the ability to configure DocInheritMeta so that special methods will have their docstrings inherited as well.
• The Methods section in a NumPy-style docstring is now recognized.