Python-ndn

- Support Unix socket on Windows 10.
- Fix semaphore running in a different event loop bug.

* Fix cocoapy to make it work on MacOS 11 Big Sur.
* Add more supports to NDNLPv2 (CongestionMark).
* Add dispatcher and set_interest_filter.
* Handle ConnectionResetError.
* Drop Python 3.6 support.

* Fix the bug that registering multiple prefices at the same time leads to 403 error.
* Add Name Tree Schema.
* Add `.devcontainer` for VSCode Remote Containers and GitHub Codespaces.

* Change the default sock file path from ``/var/run/nfd.sock`` to ``/run/nfd.sock`` on Linux.
* Add FIB and CS management data structures
* Add ``make_network_nack``
* Recognize ``NDN_CLIENT_*`` environment variables

* Fix RuntimeWarning for hanging coroutine when main_loop raises an exception.
* Fix the issue when after_start throws an exception, the application gets stuck.
* Set raw_packet of express_interest and on_interest to be the whole packet with TL fields.

* 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.