Update lifting documentation
Add -rac_setArgumentsTuple:
Change -rac_allArguments to -rac_argumentsTuple
Inline lifting signal

It was only used from one place, and it wasn't public.
Indicate signal type in variable names
Supply names to lift signals
Remove unused imports
Fold arguments accessors into property declaration
Style fix
Avoid custom property setter name
Merge pull request #761 from ReactiveCocoa/lifting-polish

Add names to lifted signals, update documentation, and other tweaks