Labels with close buttons for multi-selects.

This plugin is great but I felt the multi-select could be improved from a usability point of view. The labels are 'opt-in' via the `'labels': true` property. Refer to the last select on `test.html` for a demo.

###### Issues:
* Limited width of the select box causes many selected options to be hidden.
* Readability of comma delimited list of strings.

###### Improvements (Only for multi-selects):
* Labels are used instead of a comma delimited list of strings.
* Labels have a click-able 'unselect' button. Users can unselect options without opening the select box.
* The select box grows as more options are selected.