Added +once: and -ignore:, minor code and documentation cleanup

Fix RACDynamicSequence leaks

-collect converts nil -> NSNull, -toArray returns nil on error

NSRange support for rac_returnValue

Stream naming optimizations, fix stack clobber in RACArraySequence

Type encoding fixes, +schedulerWithQueue:name:, -rac_gestureSignal

Memory management fixes, fix RACAbleWithStart behavior, optimization

-rac_signalForSelector:, -objectPassingTest:, miscellaneous fixes

Add -all:, fix commands never completing, add -rac_didDeallocSignal

Fix -deliverOn: space usage, asynchronous -scheduleRecursiveBlock: