Now internally a full prototype system

OP_PASS implemented but not tested.
Message passing, with minor test.

Test is working, but commented out because I can’t test output until Expressions can be directed away from std::cout.
Get statement output to expression output via Universe

I don’t have a problem with this pattern, but it feels funny to have Statement using such a different one.
Implement ‘message’ keyword
Verify that single-arrow works like OP_PASS for types