Fix 'undefined' class on buttons

Fix for data attributes

Added data attributes for buttons

Patch bump

fallback to centered when triggered element is hidden

fallback to centered when triggered element is hidden

fallback to centered when triggered element is gone

Fix for positioning

had to remove target option because it's too error prone

fix for chainability (return this instead of false), added new option…

…s 'target' and 'open_now'