Example for http://stackoverflow.com/questions/36892089/how-can-i-make-bootstrap-multiselect-optgroups-collapse-by-default.

Example for http://stackoverflow.com/questions/35282650/bootstrap-multiselect-add-css-to-parent-of-selected-checkbox.

added required attribute support

typo fix

only use disabledText when multiselect is disabled

Fixed collapisble optgroups and added tests for correct mirroring and initialization of clickable optgroups.

fix optgroup uncheck accidentally unchecking its above neighbors

Implement data attributes

Fixed documentation