Simplification pass

[ailrst]

Adds the flag --simplify (which implies --parameter-form) which, after running analysis performs partial evaluation and simplification of the IR.

This usually removes the flag registers and pushes the comparisons into the assume statements where they are used, folds constants through and does some canonicalisation and term simplification.

It sits on top of the interpreter #241 for partial evaluation, and includes improvements to the parameter form which I will copy into that PR #255. When #243 is merged we should use the interpreter to validate the transform using the memory state hash the csmith examples produce. Currently this is just validated against the system tests, all of which pass with the transform applied.

this implements:

• lift registers to locals and pass everything via procedure parameters (this required adding parameters to the IR)
• a dynamic single assignment transform via variable renaming, adds an index field to local variables for this purpose so we can easily rename them without
• constant + copy propagation over the IR
• multiple term-rewriting based simplification passes
• a pass to convert 64 bit locals where only the low n bits are accessed to variables of n bits

The simplification/partial eval/copyprop rewrites are applied repeatedly with a fixed number of iterations.

For an example of what simplifications this produces: https://gist.github.com/ailrst/1b29e85a6ad891810dcc83801b1e2c6a