Extend RACAble underlaying methods by two additional arguments

These two arguments `changeKind` and `option` will allow better observation
of key-value compliant properties, including observation prior change, obtaining
previous value of the property or observation of collection mutations.
Add RACTuplePackWithNils that converts NSNulls to nils
Add variety of RACAble macros with backward compatibility

New RACAble macros for returning previous value (not only current one),
observing prior setting (the old value) and observing collection changes.
Underlaying macros and methods now accept new argument that defines when and
what objects are send from this signal.
Make KVO signal creating with types more readable

New method `+rac_signalWithChangesFor:keyPath:observer:` returns a signal, that
returns whole change dictionary from KVO. Modified method
`+rac_signalFor:keyPath:observer:type:` appends `-filter:` and `-map:` streams
depending on the given type.
Rename RACAbleTypeReplacement -> RACAbleTypeReplace
Merge branch 'feature/kvo-options' into develop
Fix detection of initial KVO observation
Added HOM version of RAC lifting

- added rac_lift and associated private RACLiftProxy.
- Refactored existing -rac_liftSelector:withObjects: and rac_lift in terms of
  common functionality. Tests pass.
- Added -[NSInvocation(RACTypeParsing) rac_argumentAtIndex:] which behaves like
  -rac_returnValue.
Added specs for -rac_lift HOM
RACLiftProxy: set NULL as return value for non-object return types
Fixed copy-pasta mistake

Was -getReturnValue:, should have been -getArgument:atIndex:
Remove all the codes
Move +rac_signalFor:keyPath:onObject: tests to RACPropertySubscribingExamples. Make +rac_signalWithChangesFor:keyPath:options:observer: behave like RACPropertySubscribingExamples
Remove -rac_signalFor:keyPath:observer:
Revert "Add variety of RACAble macros with backward compatibility"

This reverts commit 0e2f59bb4b156c8fcbe9ac8ff3c915b4f54db1a2.

Conflicts:
	ReactiveCocoaFramework/ReactiveCocoa/NSObject+RACPropertySubscribing.h
	ReactiveCocoaFramework/ReactiveCocoa/NSObject+RACPropertySubscribing.m
	ReactiveCocoaFramework/ReactiveCocoaTests/NSObjectRACPropertySubscribingSpec.m
Revert "Add RACTuplePackWithNils that converts NSNulls to nils"

This reverts commit 3a597b20083ff09a43ebeef65c314c3ba156c1bf.
Add test for sending KVO dictionaries
Add some tests
Clean up all the tests
whitespace