iso639 update

Spun out of the !117 (merged) discussion, this is a big iso639 update from the latest glibc definitions. It seems from certain parts of the diff that the VLC copy of the definitions have not been updated in a very long time, and so there's lots of improvements to be gained.

This does not replace !117 (merged).

• Fixes iso-639-2T code for Javanese.
• Fixes swapped iso-639-2[TB] codes for Greek (modern).
• Fixes names not updated since utf-8 conversion.
• Updates names of various entries.
• Many additions.
• Reformats definitions using macros to help make updates (here and in future) easier.

Note to reviewers: the work involved copying&pasting in bulk from the latest glibc definition file, and using an automated regex find&replace to reformat (add quotes to the latter params and N_() to the first). I've tripled checked it after splitting that diff across multiple commits.