Fix `invalid escape sequence '\i'` on Windows

[CatMe0w]

Fixes such errors on Windows:

C:\******\MolScribe\molscribe\indigo\renderer.py:36: SyntaxWarning: invalid escape sequence '\i'
  self._lib = CDLL(indigo.dllpath + "\indigo-renderer.dll")
C:\******\MolScribe\molscribe\constants.py:120: SyntaxWarning: invalid escape sequence '\('
  '(' + '|'.join(list(ABBREVIATIONS.keys())) + '|R[0-9]*|[A-Z][a-z]+|[A-Z]|[0-9]+|\(|\))')