examples/Mercury:
Add new grades asm_*.
wrapper.mod:
Add a new -h (help) option.
Change the behaviour of the -l option:
Exit after printing the labels
Don't use popen("sort -n"), since it's an unnecessary OS
dependency and the user can do it anyway.
[And because we weren't checking whether the call
succeeded, and I didn't want to add checking code...]
io.mod, init.h, wrapper.mod, label.c:
Remove support for automatically calling *_input.
Optimize things so that we only call init_modules() if we
are going to need the label names.
