Allow to compile modules using ARC.

This fixes the "Cast to C pointer type 'void *' to Objective-C pointer requires a bridged cast error that current customers of PSPDFKit (https://marketplace.appcelerator.com/apps/1072) are getting unless they manually edit this source file. The even better way to fix this would be to not add method bodies in a header.

Please merge this for 3.0.1, this is a major show-stopper for me and my customers