Document multicontainers

[Lartu]

There's a big issue with LDPL right now: we cannot have lists of lists, nor maps of lists nor lists of maps nor any compound type. If we had that, the language would be way more useful and a lot bunch more interesting libraries could be coded for it (and thus, used more in real-world scenarios).

I imagine the syntax would be something like:

compoundFoo is number list map

meaning that compoundFoo is a map<list>, and so we could access its members like

compoundFoo:"someKey":4 #container:key:index

[dgarroDC]

I agree that LDPL needs this, but there's a problem of ambiguity in the accessing syntax with what we already have, A:B:C could be like A[B[C]] (LDPL current syntax) or like (A[B])[C].

[Lartu]

Added in 75f7f70. Documentation still due.