I split out my AMF parsing code into a library other people can use.
It's now submoduled in.

@zhemao make sure to do "make run" in isa/ before committing

From the test comment:
sh to a word aligned address should only affect the 2 lower bytes
and should leave the 2 upper bytes unmodified.

In this test we write 2 bytes to the lower 2 bytes of the word
tdat11 and then ensure that the both the upper 2 bytes and lower
2 bytes are as expected.

We shouldn't generate a GOT.

MSIP isn't supposed to be writable locally!

For now, we no longer build hex files, because the programs don't
start at address 0.  This decision will likely be revisited.

This broadens their utility and lets them use the M-mode counters directly.