Add bcp47 subtag registery parser

[bastien-roucaries]

We need for parsing bcp47 to implement subtags parser of registery.

I volounters

[reutenauer]

I suppose you mean the plain text language subtag registry. Can you give a bit more detail of you’re thinking of? It would certainly be nice to be able to parse the registry direct from TeX (I’ve got code in Ruby that does that, by the way), but it’s also important to have a list of supported languages (necessarily much shorter than the full 7000+ languages recognised by SIL).

[bastien-roucaries]

This is the first step for parsing BCP47 tag and canonicalize.

It will be in pure latex

[bastien-roucaries]

Here the begining. I only parse the header for now but code is hard due to : being active
https://github.com/bastien-roucaries/bcptools