This document explains some of the most common operators used in ReactiveCocoa,
and includes examples demonstrating their use. Note that operators in this context
refer to functions that transform signals, not custom Swift operators. In other
words, these are the composeable primitives provided by ReactiveCocoa for working
with signals. Roughly speaking they take the shape of (Input..., Signal...) -> Signal.
Additionally, this document will use the term "signal" when dealing with concepts that
apply to both Signal and SignalProducer. When the distinction matters the inline
code-style will be used.