Compress eval_op some.
Load optab in a separate function.

Populated with example operations.
Also reverse the order of operands for non-commutative operations.
Add support for unary operations. None yet.
Implement special operator support.

i.e. an operator which does not use the stack in the normal pop/pop/push
fahsion. Delete '`' is an example (implemented).
Protect unary, binary and trinary operators from stack underflows.