General array bounds

[rooooooooob]

e.g. general (n to m elements) bounds on arrays:

foo = [n*m uint]

We already have support for the following cases:

• [* uint] (0 or more i.e. no bounds)
• [1*1 uint] / [uint] (i.e. fixed 1 element).
• [? uint] (0 or 1 - optional field) (warning: support might only be in some contexts)

There are also [+ uint] which is 1 or more but would be trivial to do if the general n*m case is done.