Add pattern-matching component type, its primitives and combinators

[blamario]

Splitters are not really the best choice for pattern-matching components. There should be a different component type for that purpose. It would still take one source and two sinks of the same type - one for the matching part of the input and the other for the consumed, but unmatched part - but it would not consume any input beyond what it needs to establish the match portion.