Improved `producer` implementation.
Improved `producer` implementation.

RuiAAPeres/ReactiveCocoa,tzongw/ReactiveCocoa,victorlin/ReactiveCocoa,sandyway/ReactiveCocoa,smilypeda/ReactiveCocoa,sandyway/ReactiveCocoa,andersio/ReactiveCocoa,victorlin/ReactiveCocoa,ohwutup/ReactiveCocoa,calebd/ReactiveCocoa,tzongw/ReactiveCocoa,walkingsmarts/ReactiveCocoa,walkingsmarts/ReactiveCocoa,rpowelll/ReactiveCocoa,rpowelll/ReactiveCocoa,andersio/ReactiveCocoa,sandyway/ReactiveCocoa,ReactiveCocoa/ReactiveSwift,ohwutup/ReactiveCocoa,ReactiveCocoa/ReactiveSwift,calebd/ReactiveCocoa,calebd/ReactiveCocoa,ikesyo/ReactiveCocoa,smilypeda/ReactiveCocoa,victorlin/ReactiveCocoa,RuiAAPeres/ReactiveCocoa,rpowelll/ReactiveCocoa,RuiAAPeres/ReactiveCocoa,ohwutup/ReactiveCocoa,walkingsmarts/ReactiveCocoa,ikesyo/ReactiveCocoa,ReactiveCocoa/ReactiveSwift,tzongw/ReactiveCocoa,andersio/ReactiveCocoa,smilypeda/ReactiveCocoa