Pancake shape improvement

[JunmingZhao42]

It seems that currently we can read from shape by index, but cannot write to shape by index. For example

fun main () {
    var hello = lds {3} @base;
    // hello.0 = 0; --> this doesn't work
    stw @base, 0;
    return 0;
}

Would be nice to write to shape by index as well (if can we can index by namestrings that'd be even better!)

[myreen]

Adding support for such assignments makes a lot of sense. I guess there should be support for nesting, ie

a.0.2.0 = ...

This should be a language construct in the Pancake AST and semantics rather than just syntactic sugar. Or rather: the construct for assignment should be revised so that this is possible.

Regarding names for fields (and shapes), yes, definitely that should be supported. The intention was never that these index numbers would be written (regularly) by humans. However, the string names should be a separate issue.