Missing license

[tmhedberg]

The lack of any license on this code may prevent it from being used in some contexts. Please consider adding one.

[alerque]

Good point.

1. First I think we need to pick a license.
2. Then we need to get all/most previous contributors to sign off on it.

Obviously in the picking the previous contributors can bring other suggestions to the table, but in this org there is already some precedent for using MIT from vim-pandoc and vim-pandoc-syntax. I'd be down with that here too. Anybody else have a license they'd like to table for this use case?