Operands was an enum covering all forms of operands and data for each
operand for all instructions. this is hard to iterate, and hard to work
with when a single operand is the one of interest, so it's now replaced
by an array of `Operand` enum instances like other architectures.

in the course of this change, several forms of decoding are broken,
while adding support for some earlier-unsupported multiplies and
  instructions like msr and clz

also clearly note which document the comments mentioning page
numbers/figures is referencing