move #callbackFactory to extend hash so it is testable, 100% coverage for this method
spec for #bindTo when target appears to be a jquery object
additional coverage for #bindOnceTo
additional coverage spec for #unbindFrom
additional coverage spec for #checkBindingArgs
#isAlreadyBound specs
Merge pull request #11 from wunderlist/WBBindableMixin-Specs

WBBindableMixin specs