Cherry picked some of the less dangerous pulls

Merged Namespacing of events https://github.com/robdiciuccio/unveil/branches/master
Merged Background image support https://github.com/shidhins/unveil/branches/bgImageSupport
Merged jquery get of image before swapping out src https://github.com/tinny77/unveil/branches/master
Merged throttling of unveils (modified) https://github.com/mstuart/unveil/branches/master