Add RACAction class as a simpler RACCommand
Deprecate RACCommand
Mark -init as unavailable for RACAction and RACPromise
Implement RACAction and -action
Collapse RAC{Command,Signal}Support categories into RACSupport
Refactor NSControl.rac_command as an example
Add RACAction to Mac static library
Reorganize and clean up project groupings

Everything's gonna conflict from my previous renaming anyways.
Tests for RACAction
Turn NSControl.rac_enabled into a bindable BOOL

This simplifies the implementation considerably.
Replace UIKit rac_commands with rac_actions
Refactor UIKit tests to use rac_action properties
Update docs with RACAction
Remove +actionWithBlock: (too confusing)
Move -action and -promiseOnScheduler: into resp. headers
LAGCHAG
Update CHANGELOG.md
Remove references to running a block
Describe intended disposal behavior for RACAction
Add disposal tests for RACAction