Adds SLSwitch

[j-mutter]

This adds an SLSwitch class which enables wraps UIASwitch's setValue method, and provides a property to access the current value of the switch as a bool instead of a string.

[wearhere]

I'm loathe to dump symbols with names as generic as "ON" and "OFF" into the global namespace. At the same time, it is nice to layer "off/on" semantics onto value. What do you think about getting rid of setValue: and just making on readwrite? setOn:YES would be pretty clear imo--that's how UISwitch is set up, actually.

[wearhere]

Hey thanks for the request @j-mutter. I really appreciate you including documentation and tests. I've made a few comments. Also, Travis doesn't yet have Xcode 5 installed, unfortunately, so the build will fail like so unless you set SLSwitchTestViewController.xib to "open in Xcode 4.6" in Xcode's right sidebar:

Thanks!

[j-mutter]

@wearhere Done. I had been using setValue instead of setOn because that's how it's handled in UIASwitch, but matching UISwitch also makes sense. And not sure how I completely spaced on the lack of matchesObject:, but that's sorted as well.

[wearhere]

Looks great! Thanks again.