Correctly handle BOOL types

property_getAttributes used to identify BOOL property as Tc.
Since Xcode 5.1, it's now being identified as TB.
This change updates LLModel to correctly handle BOOL property types.

List of all type encodings can be found on this page:
https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/ObjCRuntimeGuide/Articles/ocrtTypeEncodings.html#//apple_ref/doc/uid/TP40008048-CH100-SW1