Added KnockoutJS data-binding support 

Added KnockoutJS support by using a custom 'multiselect' binding handler.

Example:

1. Define select input
-------------------------
<select class="multiSelect" data-bind="multiselect: true,options: Options, selectedOptions: SelectedOptions, optionsValue: $data" multiple="multiple"></select>

1. Initialize Bootstrap-multiselect
-------------------------------------
$(".multiSelect").multiselect();

3 .Apply view model
Merge pull request #17 from Devristo/master

KnockoutJS data binding support.