Moved transformer out to it's own file
Made the api for transformer a little simpler, by making it's
constructor accept no arguments
Explained in the readme that the result of each transform is passed to
the next
Renamed "undo" to "reverse", forward to "up" and backward to "down"

Partly based on the naming used by activerecord migrations
Added more examples to the readme
Changed the dsl slightly, to transform.up rather than transform up

Looks more consistent, plus it makes the implementation cleaner because
we don't need an "up" method on Lou itself
Bumped the version to 0.1.0