Array of array: Implement the core functionality: types, constructors, operations.

Array of array: Implement the core functionality: types, constructors, operations.

There will be subsequent commits to refine semantics, esp. version-specific semantics,
as well as I/O functionality and restrictions.

Note: I'm getting white-space differences in the preprocessor test results,
which I'm not checking in.  I think they need to be tagged as binary or something.