Added GPUImage project to an xcworkspace.
Added run script to automatically build static framework for distribution.

- The build script was modified to dump the static framework in a
separate directory.
- A symlink to the build script was created in the Xcode project root
directory for convenience.
- An option to output versioned distributions so as to not overwrite
previous ones should be added in the future.
Added fix for mismatched hard-coded SDK version.
Added Mac project to workspace.
Added example projects to workspace.
Make .gitignore ignore all build and dist subdirectories.