xcconfig updates, add @collectionKeypath

++xcconfigs, README updates

Build settings fixes, disable -Wshadow with @strongify

Fix @synthesizeAssociations overwriting each other, ++xcconfigs

Fix buffer overflow in ext_copyPropertyAttributes()

Fix SEL casting errors on Xcode 4.6

Added armv7s to iOS architectures

Extend @keypath to support two arguments

Initial stable version