The main function is 'extractValue', which takes an operand and returns a macaw
bitvector for it (in the PPCGenerator monad).
There are still some missing cases for the memory operands.
The remaining part is 'genCaseBody', which is where we'll write the translator
from ParameterizedFormula to TH Exps. The semantics are loaded from semmc and
the outer case expression breaking down instructions is all in place. This has
several accompanying changes in semmc and dismantle.
These lists come from semmc and contain the bytestrings of the semantics files
for each opcode.
NOTE: The lists are currently empty (presumably due to bugs), but the logic for
moving data around and setting up a SimpleBuilder instance is at least right.
