v0.3.0

• New method: FlagWrap.is_valid_meaning for convenience.
• Change reduce method to exclude entire flag vectors (all bits) from reduction if any bits in
  the exclude_mask are set.
• Make FlagWrap.flag_meanings "public" (prev. FlagWrap._flag_meanings)
• Adds name attribute, available from init as kwarg, for misc use.
• Drops support for Python 2.7