v0.2b2

• Switch to Apache License 2.0.
• Add NDNApp.get_original_packet_value.
• Improve NDNApp.route and NDNApp.express_interest to give access the
  original packet and signature pointers of packets.
• Fix typos in the documentation.
• Support more alternate URI format of Name Component (seg, off, v, t and seq)
• Update Python version to 3.8 and add PyPy 7.2.0 in GitHub Action.
• Fix Name.to_str so its output for [b'\x08\x00'] is correct.