First pass at a generic RACBinding wrapper for AppKit
Skip the initial model value, not the view's
Basic tests for -rac_bind:options:
Manually trigger bindings in unit tests
Refactor implementation of -rac_bind:options:
Lifecycle tests
No need to log on property subject errors

It happens already within the implementation of RACPropertySubject.
Test that observable property subjects complete
Test that RACBindings propagate completion
Forward completion in bindings and property subjects
Allow bindings to terminate their property subjects
Additional lifecycle and completion tests
Deprecate old AppKit binding methods
Note that two simultaneous bindings is undefined behavior
Test manual completion of an AppKit RACBinding
Add test which reproduces the issue #651
Overwrite super's designated initializer
Merge remote-tracking branch 'origin/2.0-development' into appkit-bindings-proxy
Clarify `completed` events on RACBinding
Test `completed` in RACPropertySignalExamples