Python 3.12 support

[jairhenrique]

• Add support to python 3.12
• Fix code warnings

inflector/languages/base.py:48: SyntaxWarning: invalid escape sequence '\/'
  return  re.sub('[^A-Z^a-z^0-9^\/]+', '_', \
inflector/languages/base.py:49: SyntaxWarning: invalid escape sequence '\d'
  re.sub('([a-z\d])([A-Z])', '\\1_\\2', \

[ixmatus]

@jairhenrique can you remove 2.7 from the test matrix? I think 2.7 is long unsupported at this point and it's fine to no test against it anymore.

[jairhenrique]

@ixmatus done!

[paulcwatts]

Is it possible to get a new release with this?

[ixmatus]

@paulcwatts I released to pypi: https://pypi.org/project/Inflector/3.1.1/.