Macro Chain 

macro_rules! Chain {
    ($single:ty) => { ... };
    ($first:ty, $($rest:ty),+ $(,)?) => { ... };
}

Combines processors into a serial chain.

Single processor optimization:

Chain![MyGain]  // Compiles to just `MyGain`, no wrapper overhead

Multiple processors:

Chain![Gain, Filter, Limiter]  // Nests as Chain<Gain, Chain<Filter, Limiter>>