Thanks to @hirbod from Issue #1 for inquiring about creating a refresh method.
If you are using async scripts, or want to be able to dynamically add multiselect elements later on, go ahead and call multiSelect() or window.multiSelect.refresh() to initialize newly appended .multi class elements. Refrain from using document.body.innerHTML as this removes the event listeners from the multiselect element buttons. Feel free to contribute to this project, or voice your comments in the issues, and I will get back to you right away.
Cheers
Jacob