comment.
refactor expand_macro.
expand_macro -> run_macro.
Trace passed but not used.
moved Step back to run.h.
comments; removed useless assertion.
run_step_disp passes code.
preliminary support for llvm-cov.
move forward declarations.
tco_call (unused).
trace.
exc_trace prints code objects.
types are now first-class objects; type symbols removed.