Fix warnings

When building with some unnamed newer SDK, we get a handful of warnings.  Namely:

- Use `NSTextAlignment` instead of `UITextAlignment`.  The enums line up, so it's a safe replacement
- `NSString`'s `sizeWithFont:` is deprecated
- `NSString`'s `drawInRect:` is deprecated
- `UIView`'s `contentStretch` is deprecated

In addition, the demo app won't run b/c the compiler is hard coded to llvm-gcc4.2.  I switched this to the default (llvm 5.0 for newer Xcode's and whatever the default is for Xcode 4)

All of the changes have conditional compilation, so it still uses the old way if you're targeting 6 & below.