Fix invalid escape sequences in Regexes causing SyntaxWarnings in Python >=3.12

[Ferdi265]

This fixes issue #75 by correctly using raw strings (r'') for these regexes.

[lucc]

Hello @aclements do you mind merging this? It is becoming an annoyance because distributions have switched to python >=3.12 which emits a syntax warning for this. (python 3.15 even says "Such sequences will not work in the future.", which I read as a deprecation warning)