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

this is a squash of a few months' hacking, including but not limited to
what eventually got extracted into
https://git.iximeow.net/asmlinator/about/

the path here is generally not historically interesting, and the vast
majority of this diff is very particular static data tables
(BehaviorDigests and implicit operand lists)

`src/long_mode/behavior.rs` will more or less be directly adapted into
versions for x86-32 and x86-16, similar to the instruction decoders.