Reduce code size.

Frame-relative references consume a lot of code space.  This patch replaces
frame-relative parameter passing with parameters passed via global variables.
This reduced the (current) STS image from 1732 bytes to 1272, saving 460 bytes,
or just about 26% of space.  Frame-relative parameters will still be necessary
when it's time to pass parameters between transient program modules and the
operating system.  However, this can be done only once (at the program/OS
interface boundary), which will consume much less memory than simply using it
everywhere.

A pity, really -- frame-relative addressing is very convenient.