Generate TZ.h from zoneinfo

Using tzdata pypi package that ships zoneinfo blobs
Can't use raw data package from IANA, need it built first
Minor tweaks to Espurna script that generated .md

More data than the original, not limited to ZONE/...
Zoneinfo source can be overwritten using path args, if needed
(but, probably not needed, since it would always be preferable to pull the latest version)

Also, allow to override certain names and tz strings independent
of tzdata values (resolves #9007)

Author: mcspr