Unicode 12.1 Support

[Harmon758]

https://www.unicode.org/versions/Unicode12.1.0/
http://blog.unicode.org/2019/05/unicode-12-1-en.html
python/cpython@3aca40d
python/cpython#13214
https://bugs.python.org/issue36861

[anthrotype]

It would be nice to have a shell script to automate the process of updating the UCD data and synchronizing with latest CPython source. Or perhaps document how this is done manually.

[Harmon758]

It's primarily just updating UNIDATA_VERSION in both makeunicodedata.py and makeunicodedata3.py, and then running both scripts with Python 2 and 3, respectively. I then copy the expected_checksum for test_unicodedata2.py from the matching change to test_unicodedata.py in the corresponding CPython commit. After that, I run the tests and make sure the changes to the database match the CPython commit.

At this point, besides for documentation, the changes should fully match the CPython commit.
If there were any additional changes to makeunicodedata.py or test_unicodedata.py, those would need to be manually matched before running the script or tests. (In this case, in #30, I matched python/cpython@6fec905 as well, as that change was made prior to the Unicode 12.1.0 update.)

Finally, I update the changelog, the readme, and the version number in setup.py.

[anthrotype]

Thanks for the info! It looks like most of that could be automated. Maybe for next time then :)