Deprecation warning due to invalid escape sequences in Python 3.7

[tirkarthi]

Deprecation warnings are raised due to invalid escape sequences. This can be fixed by using raw strings or escaping the literals. versioneer file is autogenerated and has an issue upstream.

find . -iname '*.py' | grep -v example | xargs -P 4 -I{} python3.8 -Wall -m py_compile {}
./versioneer.py:97: DeprecationWarning: invalid escape sequence \s
  LONG_VERSION_PY = '''
./pretty_bad_protocol/_parsers.py:846: DeprecationWarning: invalid escape sequence \d
  allowed_entry = re.findall('^(\d+)(|w|m|y)$', self._expiration_time)
./pretty_bad_protocol/_meta.py:57: DeprecationWarning: invalid escape sequence \d
  _VERSION_RE = re.compile('^\d+\.\d+\.\d+$')
./pretty_bad_protocol/_util.py:129: DeprecationWarning: invalid escape sequence \d
  _VERSION_STRING_REGEX = re.compile('(\d)(\.)(\d)(\.)(\d+)')