Convert linguist data into Go code

GitHub's linguist project is the most accurate and best maintained
database of programming languages and file types that I know of.  Both
ack and silver searcher spend way too much time maintaining their own
list of languages.  We'll just leverage GitHub's work.

This converts linguist's YAML file into a Go variable that maps a
language nickname to details about that language.  These details should
be enough to select matching files from a directory tree.