add iOS library and framework targets for TouchDBListener

[pegli]

This pull adds two new targets to the project:

Listener iOS Library: iOS static library for the Listener files
Listener iOS Framework: Framework file that wraps the Listener iOS library

I'm currently using the framework in my own project and it has been working fine. Note that the iOS listener framework doesn't depend on the TouchDB iOS framework explicitly, but feel free to change that if you like.

Thanks!

[snej]

Thanks again! I've got it merged in locally.
I just need you to fill out a Couchbase committer agreement, to make it explicit that we have your permission and you own the rights to the code. The easiest way is to register on our code-review server at http://review.couchbase.org/ ... let me know once you've done that.

[pegli]

Done!

[snej]

OK, it's pushed! Thanks again.