Added block method that gets called when config is ready

This adds some support to be notified when LaunchKit Config is ready (has received data from the server)

Usage measurement tools (debug), and API call improvement

This adds some debug usage measuring tools, as well as a reduction to the already light network bandwidth usage.

Added Carthage Support

LaunchKit is now available through Carthage. Add the following line to your Cartfile:

github "LaunchKit/launchkit-ios"

Bug Fixes

Included some missing framework imports, and fixed some comments 👍