Disassemble a few Thumb instructions.

Disassemble.hs doesn't actually do anything with this yet, but if you
play around in ghci then you can totally disassemble Thumb!  Or at
least, certain Thumb branch instructions!

ARM.hs and Thumb.hs have pretty much exactly the same structure and
anything using them will also have to basically write the same
functions twice.  I should probably look into typeclasses??  Or
something???