Added option for #466 - although this may be handled easier by directly modifying the buttonText option!

-> Added setAllSelectedText function to set the text displayed when all options are selected dynamically at runtime
-> Updated doc

-> Added an overflow: hidden and text-overflow:ellipsis to the button CSS if a buttonWidth is specified
-> Updated doc

Updated documentation. In short: #380, #365, #381, #377, #385, #384, #388, #302, #305, #391, #374, #397, #400, #375, #383, #301, #382, #386, #387, #404.