Transition options undocumented, possibly broken

The feature was merged [here](https://github.com/flaviusmatis/easyModal.js/commit/8534d9914a8bdc79e63919385c079f1d6a9644e4) 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.)

Start by reading commit 8534d9914a8bdc79e63919385c079f1d6a9644e4, which introduced the transition options, and inspect how transitionIn, transitionOut, and closeButtonClass are documented and applied. Reproduce the cases described in the issue, especially using both transition options together. Done means the options are documented and the reported close-button behavior is either fixed or clearly characterized.

Written by the indexing model from the issue text.