Regex SyntaxWarnings

[trenslow]

In Python 3.12 we're now getting SyntaxWarnings at runtime, i.e.:

/opt/venv/lib/python3.12/site-packages/panphon/segment.py:12: SyntaxWarning: invalid escape sequence '\w'
   """Constructs a `Segment` object that models a phonological segment as a vector of features.
/opt/venv/lib/python3.12/site-packages/epitran/cedict.py:25: SyntaxWarning: invalid escape sequence '\s'
   comment_re = re.compile('\s*#')
/opt/venv/lib/python3.12/site-packages/epitran/cedict.py:26: SyntaxWarning: invalid escape sequence '\['
   lemma_re = re.compile('(?P<hanzi>[^]]+) \[(?P<pinyin>[^]]+)\] /(?P<english>.+)/')
/opt/venv/lib/python3.12/site-packages/epitran/rules.py:44: SyntaxWarning: invalid escape sequence '\s'
   if not re.match('\s*%', line):

This was elevated from a DeprecationWarning in previous versions of Python, and they plan to make this a hard error in future versions.

I believe it's an easy fix by simply making the strings a raw string. I would be willing to submit a PR, but the versions between PyPI and GitHub don't line up, so I'm not sure where to branch off. The first line even is a warning from Panphon, so I could also make a fix there too.