Add -rac_liftSelector:withObjectsFromArray:

Refactor -rac_liftSelector:withObjects: to become wrapper around
-rac_liftSelector:withObjectsFromArray.
Add -rac_liftBlock:withArgumentsFromArray:

Refactor -rac_liftBlock:withArguments: to become wrapper around
-rac_liftBlock:withArgumentsFromArray.
Extract lifting strategy into RACLiftAndCallBlock()

This change extracts the lifting logic common to -liftSelector and -liftBlock
into a single function.

Implemented as a static function to avoid needlessly adding methods to
NSObject.
Assert argument count in -rac_liftSelector:withObjectsFromArray:
Document *FromArray variety of lifting methods
Replicate method lifting specs for *FromArray variety

Copy the specs for -rac_liftSelector:withObjects: and
-rac_liftBlock:withArguments: and adjust to test the *FromArray alternatives:
-rac_liftSelector:withObjectsFromArray: and
-rac_liftBlock:withArgumentsFromArray: respectively.
Add method lifting tests around handling nil
Use @unsafeify over @weakify

For AppKit compatibility.
Correct format string types
Make RACAble macros slightly easier to read
Added a separate method to observe with an initial value

Also fixed keyPath copying and added some parameter assertions.
Use -rac_signalWithStartingValue… for RACAbleWithStart()
Unit test
Merge branch 'master' into lift-with-arguments-array

This merges in the changes from #424.

Conflicts:
	ReactiveCocoaFramework/ReactiveCocoa/NSObject+RACLifting.h
	ReactiveCocoaFramework/ReactiveCocoa/NSObject+RACLifting.m
	ReactiveCocoaFramework/ReactiveCocoaTests/NSObjectRACLiftingSpec.m
Follow array literal conventions
Make local copy of arguments prior to lifting signals
Create new documentation for Obj-C operators.

I spent much time until finally understood how exactly do basic operators work and why we need them. This post was intended for my blog, but maybe it can be useful for other newcomers here, in documentation. You are welcome to reject the patch if this information is not appropriate. Thanks!
Improve description for some methods.

Coneko proposed great changes to the original document, so here they are.
Improve description for Linear Operators.
Merge pull request #442 from ReactiveCocoa/defer-kvo-start

Only read RACAbleWithStart's initial value upon subscription