this includes a `Makefile` that exercises the various crate configs.
most annoyingly, several doc comments needed to grow
`#[cfg(feature="fmt")]` blocks so docs continue to build with that
feature enabled or disabled.

carved out a way to run exhaustive tests; they should be written as
`#[ignore]`, and then the makefile will run even ignored tests on the
expectation that this will run the exhaustive (but slower) suite.
exhaustive tests are not yet written. they'll probably involve spanning
4 byte sequences from 0 to 2^32-1.

also remove redundant assignments of operand_count and some OperandSpec,
bulk-assign all registers and operands on entry to `read_instr`. this
all, taken together, shaves off about 7 cycles per decode.

this is... a more significant rewrite than i expected yaxpeax-x86 to
ever need. it turns out that capstone is extremely permissive about
duplicative 66/f2/f3 prefixes to the point that the implemented prefex
handling was unsalvageable.

while this replaces the *0f* opcode tables, i haven't profiled these
changes. it's possible this is a net improvement for single-byte
opcodes, it could be a net loss. code size may be severely impacted.
there is still work to do.

but this in total gets very close to iced/xed/zydis parity, far more
than before.

also adds several small extensions, gfni, 3dnow, enqcmd, invpcid, some
of cet, and a few missing avx instructions.