Added user support to CMB2 Meta Split

CMB2 Meta Split updated to work with users too.

Missing feature

I've updated the CMB2 Meta Split plugin to fully support users too.
Support for repeatable or group fields on users was missing and I just had to add it.
The plugin is simple in its inner workings and will take care of saving a split copy of the post or user meta along the serialized one Custom Meta Boxes 2 would normally save to allow for meta queries to work.
Searching in serialized meta values is not a feasible and performing way to do any scalable search and I was missing the feature.
The need for a serialized copy of the meta remains as the order the meta is inserted with might be relevant; the plugin is still in early stages so space is ample to make it better.

On GitHub

The plugin is on GitHub free to use.

Next

The plugin footprint lends itself to some testing trials I've tried to tamper with for a while: I will do some database testing to cover actual features and find new missing ones.