[do not merge] work-in-progress dead code elimination

[0adb]

Work on implementing a compiler phase for replacing SSet's, SLit's and SOp's that target variables that are unread later in the function (or not live) with SSkip. Currently first pass of implementation is done, still need to work on proof of correctness. Attached are screenshots of diffs of assembly code in compilerExamples/deadAssExample.v