Add swappable animation functions

Right now, when you call `Mouse.move_to` the animation is a straight from start to finish. It  would be nice if `Mouse.move_to` supported an additional argument that matched to an animation function, or perhaps take a block.

``` ruby
Mouse.move_to [10, 10] # default
Mouse.move_to [10, 10], :bezier
Mouse.move_to [10, 10], :wacky
```
