UltiSnips/generate.py:
Dropping python2 support.
Modularizing the retrieval of files, the retrieval of docstring
information, the creation of per-module snippet strings and the writing
of the snippet file.
Making the sorting of files and module options and their parameters
implicit.
Introducing string replacements based on reserved chars in UltiSnip's
tabstops.
Adding documentation to all functions.
Black formatting code.
UltiSnips/generate.py: Dropping python2 support. Modularizing the retrieval of files, the retrieval of docstring information, the creation of per-module snippet strings and the writing of the snippet file. Making the sorting of files and module options and their parameters implicit. Introducing string replacements based on reserved chars in UltiSnip's tabstops. Adding documentation to all functions. Black formatting code.
Closes #104