`meta` package fate

This is a follow-up for https://github.com/rejectedsoftware/vibe.d/pull/347

1) I have updated existing `extractUda` functionality to incorporate information from utilities @japplegame pull and renamed it to more clear `findFirstUDA`.
2) Whole package was moved to `internal` block.

Intention is to prevent any direct usage by applications outside of vibe.d and slowly integrate functionality into Phobos when it seems fitting. Stuff that won't look good in Phobos will be collected as-is and eventually separated into own library or merged with some existing one (it is a unclear long-term goal).

Sounds OK?