this includes `trait DisplayRules` as a generic mechanism to control
parts of instruction printing, a `DefaultRules` for the existing
formatting style, and `AbsoluteAddressFormatter` to print instructions
as at some location in an address space.

this includes a mildly nightmarish bit of test harness to compare
against ml.exe/ml64.exe/dumpbin.exe, which in turn chased out a bunch of
bugs. yay!

these all existed since forever but the library did not distinguish them
and did not provide prefix information for users to tell which had been
decoded.

along the way, fix an error: maskmov is memory read-write.
additionally, operand information about {push,pop}a{,d}.