Ability to customise the close icon

[jaxtheking]

Hi, just came across this library and I think it's great. With the plethora of modals out there, yours stands out mainly for its simplicity. I need to customise the close icon (X) to match the designs I'm working on, but I see the SVG code is embedded in a JS private method. Would you consider exposing the closeIcon method so that developers can use their own SVG?

Thanks, Luca