It was previously decided that, since the language is not to be
Turing-complete, a loop that takes a variable for its upper bound
should use the variable's value at the time of the loop's start, not
look it up. I forgot this while writing the syntax->IR compiler, so
loops with non-constant stop counts failed to compile.
It replaces the IR-FETCHVAR's result with the variable being
fetched. This only works when the only use is in an operation that
does not require a separate fetch be performed, such as those
implemented as CPU instructions.
The compiler middle stage takes high level nodes and produces code in
an intermediate representation more closely resembling assembly code.
Optimizations and the tools for making those are also included. It's
significantly easier to optimize IR than syntax trees or assembly.
Several things need cleaning up, in particular there are things in
jigs.lisp that really should be documented tools, not
jigs (specifically the compilation setup and finalization).
