Automatically generate evaluation code; see full log

This adds a simple pre-compile system to generate code for several operations.
The standard arithmetic and logic operations and compound arithmetic/assign
operations.

Currently the code is still restricted in the types it handles but this will
be expanded upon later.
Cleanup some unused code, some cerr -> throw
Replace hard-coded !for with pbrane- !do; see full log

Everything that is needed for !do is not yet implemented.
!eval will evaluate its argument, and will allow !do to work.

!sl uses string-int multiplication which is not yet implemented correctly.