Add 1 new method 'toggle', 2 new events 'onOpen' and 'onClose', and 1 new option 'searchBeginsWith'

Commit 1 adds a new method, 'toggle' to programmatically open and close a bootstrap-select drop-down, eg:
$('.selectpicker').selectpicker('toggle');

Commit 2 adds two new events 'onOpen' and 'onClose' so that user can subscribe in the options of bootstrap-select like so:
$('.selectpicker').selectpicker
(
  {
    onOpen : function()
    {
      alert("now open");
    },
    onClose : function()
    {
      alert("now closed");
    }
  }
);

Commit 3 adds some more 'onClose' hooks so it works properly on key events.

Commit 4 adds an option 'searchBeginsWith' which when set to true does a LiveSearch only from beginning of the word, more like autocomplete.