help2man is an improved version of the tool available on Linux. It
has a few bugs fixed.
help2md is based on help2man and converts the python --help and
--version output to a markdown help page.
This improves the implementation for normalizing language tags
when installing a keyboard. Based on the Windows implementation
in `Keyman.System.CanonicalLanguageCodeUtils.pas`.
One difference to the Windows implementation is that the mapping of
3- to 2-letter tags is based on `langtags.json` instead of
`iso639-3.tab`.
Closes#3399.
