Transition options undocumented, possibly broken

[su]

The feature was merged here from @siamkreative back in March.

1. They're undocumented.
2. They call for classnames, but need them specified differently from the existing features, eg. closeButtonClass calls for the format ".classname" but the transition options need the class without the leading period or it also gets inserted into the element class attribute.
3. Using transitionIn or transitionOut individually is fine, but if you specify both of them, the close button(specified with closeButtonClass) no longer works, for no reason I can figure out. (I don't have time at the moment to dig into this.)

[siamkreative]

Feel free to create a pull request for everything you mentioned :) I'll try to look at it but I'm pretty busy at the time.

Cheers

[siamkreative]

I added a quick demo: #23