More handy verbs, e.g. Vector join (I'd previously had Single join)
soon going to allow plotting of multiple streams
yay for symmetry between sing and multi streams
Start unpicking macro version of term chaining.
The goal is to collapse out the "macro" compilation unit.
Also move to the general "Term" interface, rather than the MacroTerm implementation.
This will allow general expression construction, analysis and refactoring (e.g. identify partial parallelisable expressions, send them to grid workers, and recombine locally).