Rename vim grammar to reduce confusion.

This change has been overdue. One of the last vestiges of the project being quick hacks I used that I didn't plan on publishing:-) verbal_emacs as the name of a VIM grammar is confusing, especially now that someone's working on an actual emacs grammar.

Unfortunately, if you are using the vim grammar and have modified your vocabularies from the default, you will need to update the tags (see the example configs for details).