Custom model request

[Catalin-Avram]

Please allow for custom convertToSelect2Model and convertToAngularModel functions to be specified in the options object. Seems the easiest way to allow advanced uses of this without making a million other options and if else conditions.
My use case is similar to the simple_tags option in that I just want to feed it a simple array of strings, but I would like the ids to be the array index rather than the text itself (for multilingual support reasons).
Would be nice to have this functionality built in so I can use this library from a CDN.

[kennethlynne]

+1

[devilankur18]

+1

[devilankur18]

Pull request: #229