acorn 6 and acorn-loose

Hi

Acorn 6 just released, and acorn-loose is a seperate package now.
I plan to send a PR to add these two parser.
But not sure how to name it.

My idea now is:
* Current acorn rename to acorn 5
* Add new acorn (version 6)
* Add new acorn-loose (version 6)

But this naming is not align with other parsers, ex babel-eslint.
Do you have any idea?

No files or tests are named. Start by reviewing existing parser entries and the naming convention used for parsers such as babel-eslint, then decide how Acorn 6 and acorn-loose should fit. Done means an agreed naming scheme and, if pursued, support for both parser packages.

Written by the indexing model from the issue text.