A signal is a structure that can yield an infinite amount of data. The API is very similar to `std::iter::Iterator` but with the assumption that it will never end. # Example ```rust use langis; let my_signal = langis::square( langis::constant(0.25) ); loop { assert_eq!(my_signal.next(), 1.0); assert_eq!(my_signal.next(), 1.0); assert_eq!(my_signal.next(), -1.0); assert_eq!(my_signal.next(), -1.0); } ```