Add mixin support to core extension...
Add mixin support to core extension...

Allow createPlugin to support composing the API
through mixins via createMixin and applyMixin(s).
Also allow support for commands. Also add core
mixins: data, event, selection. The usage details
will be in forthcoming documentation.

Refactor and expand createPlugin's API-additions
and createInstance logic, with the latter going
into a separate method.
hlfcoding/hlf-jquery,hlfcoding/hlf-jquery