Remove couch related requires.
Remove couchdb dependencies.
Remove couchdb storage class.

Moved to vines-couchdb gem.
Remove sql related requires.
Remove sql storage class.

Moved to vines-sql gem.
Remove activerecord dependency.
Remove mongo requires.
Remove mongodb storage class.

Moved to vines-mongodb gem.
Remove mongodb dependencies.
Remove redis storage require.
Remove redis storage class.

Moved to vines-redis gem.
Require json to get Hash#to_json method.
Remove sqlite3 dependency.
Move couchdb settings to vines-couchdb gem.
Move mongodb settings to vines-mongodb gem.
Move redis settings to vines-redis gem.
Move sql settings to vines-sql gem.
Point to other storage gems for config settings.
Load available storage backends.
Update minitest to 5.0.4.