docs: def extract_version(filepath='jeni.py', name='__version__'):
      """Parse __version__ out of given Python file.
  
      Given jeni.py has dependencies, `from jeni import __version__` will fail.
      """
      context = {}
      for line in open(filepath):
          if name in line:
              exec(line, context)
              break
      else:
          raise RuntimeError('{} not found in {}'.format(name, filepath))
      return context[name]