Make sure to remove the correct callback

When providing a callback to remove we should remove that from the
array not the last element.  Whoops.
Do not call addEvent from Gator.off
Improve Gator.off. Fixes #5

- Make it so Gator.off does not error if you call it before events
are bound
- Add ability to call `Gator(element).off()` with no arguments to
remove all events associated with the given element
- Add documentation explaining what is happening
Increase version to 1.2.0
Add minimized version