RACSequence addition added to NSIndexSet
Reive notes taken into account, small odds fixed
NSIndexSet sequence additions TestSpec fixed according to Notes
Refactoring: buffer copying optimized. Formatting fixed.
Documentation added. Public header added to common headers list.
Small modifications according to review notes
Make NSIndexSet+RACSequenceAdditions public
Remove umbrella import from RACIndexSetSequence
Simplify RACIndexSetSequence with derived variables
Various style fixes
Merge pull request #1031 from ReactiveCocoa/pr/1019

NSIndexSet.rac_sequence redux