docs: def find_version(filename):
      """
      Find package version in file.
      """
      import re
      content = read(filename)
      version_match = re.search(
          r"^__version__ = ['\"]([^'\"]*)['\"]", content, re.M
      )
      if version_match:
          return version_match.group(1)
      raise RuntimeError('Unable to find version string.')