make README.md clearer
Update README.md
refactor: use semicolons

because conservatives :)
refactor: $bg should not be dollar variable

beause it's not a jquery object, we shouldn't be using prefix the var
with `$`.
refactor: if/else structure

i've changed tastes
refactor: simpler way to retrieve background image url
remove unnecessary semicolon
refactor: add semicolons to index.html

because conservatives :)
add support for background-size: cover

To determine the dimensions of the image when the background-size is set
to cover, we first compare the aspect ratio (width/height) of the image
with that of the element. If the image's aspect ratio is greater than
the element's, we know that it is fatter than the element and so the
scale would be set by the ratio of their heights. The opposite is true
if the image's aspect ratio is less than that of the element.

Note that there 'cover' is just one of the many ways we can specify
background-size and we haven't taken into account of the others.
remove unnecessary var declaration
update version to 1.2
refactor: define plugin class

This refactoring will ultimately allow us to call methods on elements
that had draggle background enabled. For example, we could add a method
to disable the draggble background feature bound to the element.

For this, we define the Plugin class and save an instance of it onto the
element's data attribute provided by jQuery.
indentation
refactor: rename $this to $el

shorter and more indicative of what it is
add disable feature
update version to 1.2.1
Add a 'done' callback

Add 'done' callback for when dragging is complete
Move check for background-size: cover inline

I had an issue where I was setting the size after image load and checking immediately was failing for me.
Add mouseleave event for unbinding drag

When dragging background and mouse leaves the outer div
Merge pull request #10 from jeffsaracco/master

Fix bug with background cover - add mouseout - add done callback