Change to explicitly specifying architectures as armv7, armv7s and arm64.

This adds armv7s over the Xcode 6 standard architectures.
The library can now be linked with with apps that include an armv7s slice.
Fix NSShadow customization option implementation
Merge pull request #316 from douglashill/architectures

Fix library failing to link when compiling app for armv7s.