Added color animations and show/hide features, relative sizes and anim control (skip/pause/resume)

- implemented color animations (color name, hexadecimal or RGB notation are accepted)
- show, hide and toggle methods display or hide elements by animating "height", "width" or "opacity" properties
- values like "+=50px" or "-=5%" are accepted
- skip, pause and resume methods for both animations and queues are provided.
- some minor code improvements