Correct position/width of span if the element is not visible

Fix #44 (https://github.com/adamcoulombe/jquery.customSelect/issues/44)
Added grunt file to handle minification.
Added amd and commonjs wrapper
Merge commit '61dd3857919c8e70ffee45d42ebc10341a50d5f9'

Conflicts:
	README.md
	jquery.customSelect.js
	jquery.customSelect.min.js
Added demo to index html to show it works when applied to a hidden select