def clip_at filename, position
      position = Position.normalize(position)
      SourceMap::Clip.new(self, cursor_at(filename, position))
    end
def clip_at filename, position
      position = Position.normalize(position)
      SourceMap::Clip.new(self, cursor_at(filename, position))
    end
Get a clip by filename and position.

 @param filename [String]
 @param position [Position, Array(Integer, Integer)]
 @return [SourceMap::Clip]