Access inner variables

[Michael-K-GH]

Allow access of a previously-declared variable's child values in length specifiers and conditions.
Proposed syntax uses dot-notation:

struct MyStructType {
    some_value : Int;
}

...

some_struct : MyStructType;
an_array : Byte[some_struct.some_value];

if (some_struct.some_value == 7) { ... }