Fix OS X framework target.
Fix framework search paths and linking with Cocoa.

- For the OS X framework target and the unit test targets.
Change the name of the build products.

- They are now `Masonry.framework` for OS X and `libMasonry.a` for iOS.
Fix some more linking and searching for frameworks.
Merge pull request #11 from rastersize/fix-osx-target

Fix OS X target