Hierarchical outputs from branches

[jacg]

Currently we have

pipe([out.Y], out.X) -> Namespace(Y=<branch output>, X=<main output>)

which is great, but then

pipe([out.X], out.X) -> Namespace(X=(<branch output>, <main output>))

which is not so good.

You might say "so don't use the same output name twice in the same network!" but that's easier said than done:

abstraction = [out.X]
pipe(abstraction, out.X)

Might these issues be mitigated by enabling hierarchical naming for branches?

Maybe something like

pipe(out.B([out.X]), out.X) -> Namespace(X=<main out>, B=Namespace(X=<branch out>)

This might form part of a solution to #17.