Exploratory CPU backend

This MR accomplishes the following:

• Compute anti-dependencies between array reads and writes in IR
• Identify logical array allocations - this identifies the size of each individual allocation, and which nodes use which allocation
• Create an incomplete LLVM IR backend for Hercules IR - uses the Inkwell library
  • Inkwell is not feature complete - we will want to emit IR text manually in the future
• Incorporate anti-dependencies into global code motion
• Various helpers for IR - iterators for dominator tree, types, constants
• Remove bitflip op - just not on an int value
• Improve dot graph layout

The matmul.hir example can now be compiled into LLVM IR. When hooked up with some manually written C, it does a matmul properly.