Switch from re to 3rd-party regex module

[Seirdy]

Switch to the more featureful, API-compatible regex module. This module is recommended for more advanced regular expressions in Python's own documentation: https://docs.python.org/3/library/re.html

Regex patterns can now use features such as variable-length lookarounds, lookarounds in conditional patterns, recursive patterns, fuzzy matching, \m and \M for the start/end of a word, and many others. See https://pypi.org/project/regex/ for more information.