This commit adds a new script, generate-wcwidth.py, that generates
wcwidth tables from the bundled files (Unicode 14.0):
* DerivedGeneralCategory.txt
* EastAsianWidth.txt
This commit also adds the functions my_wcwidth() and my_wcswidth()
that replaces the system’s wcwidth()+wcswidth(), and uses the
generated tables to map Unicode codepoints to widths.
This is inspired by both XTerm’s wcwidth implementation, as well as
https://github.com/jquast/wcwidth.
Both of those are based on/inspired by
https://www.cl.cam.ac.uk/~mgk25/ucs/wcwidth.c
