Fix -dealloc swizzling not noticing new superclass implementations

Add missing import, fix casting warning, improved lifting docs

First release candidate for RAC 2.0

Various critical fixes

-concat bug fix, documentation improvements

Added -throttle:valuesPassingTest:, Xcode fixes

Fix disposed subscriptions getting events, improve dealloc disposal

Fix -concat dropping signals and not always disposing

Optimizations

Fix rac_command concurrency, only run -rac_description in DEBUG