Functions can now be used as arguments

Each function gets assigned an ID and can be retrieved into the stack
using 'GETL <ID>' instruction.

* Dump now prints instruction names in UPPERCASE for clarity
* A minor change in 'main' to aid debugging. See diff
The DEF instruction added

isFunc checking removed as no one would really use it (I'm sure!)

DEF instruction accepts a string to which to assign last stack
element.