fix optgroup uncheck accidentally unchecking its above neighbors

Implement data attributes

Fixed documentation

Added better knockout documentation.

website overflow issues fixed

Added tests to clarify that selectedOptions is what
 to use when you want to update the checked state of
 multiple options.

Fixed #575. The select all is not triggering the onChange anymore. Only the onSelectAll is triggered.

Add support for the KO enable/disable bindings.

Fixed trigger onSelectAll run.

selectAll() does not 'select' options with data-role='divider'.

deselectAll should do so in singleselect as well.