Add support for the trie.map method

[duilio]

map restores an instance of a Trie from memory.

[duilio]

I've just realized the test suite doesn't run against Python 2.x, I've only added the PY2 compat code for the buffer protocol because I saw the Python 2 classifier in setup.py, I guess it would be better to remove the compat code and the classifier which is there probably for legacy reasons?

[BoboTiG]

You are right, it's time to say goodbye to Python 2.

Do you think you can do it in a separate PR (if you was thinking about doing it yourself, of course)? I'll do it :)

[BoboTiG]

OK that's done in #91. If you can rebase your branch then, I'll unlock the CI.

[duilio]

@BoboTiG branch rebased. ;-)

[BoboTiG]

Thanks a lot @duilio 🍾