Fix a couple of issues: [#26]
- Setting cssReset option would break both close icon and escape key
- Ugly filter

This also allows user to listen to a click on '.featherlight-close' and
act on it, and this will work independently on how the dialog was closed
(icon or custom button).
Updated readme
Merge branch 'master' of github.com:noelboss/featherlight
Simplified code and updated formating