- Removes nullability shims for Xcode 6.
- Removes MGLTypes.h from files where it was only being used for
nullability support.
- Accepts that `NS_SWIFT_NAME` is not fully supported by Xcode 7.2 and
lower.
- Adds documentation about Xcode 7.3 requirement.
Reformatted documentation comments in public headers in the OS X SDK and public headers shared between the iOS and OS X SDKs to wrap at column 80 and avoid excessive indentation that causes SourceKitten to detect code blocks.
