Improve evaluator / find new LLVM wrapper

[chemix-lunacy]

Inkwell support for certain things was patchy and some of the getelementptr features had to be done directly via LLVM-sys.

Things which need to be fixed:

1. getelementptr needs to be centralized and made to work. Can't get a GEP instruction or follow it in Inkwell when it's an argument without dropping to the LLVM-sys object.
2. Get the SSA identifier from instructions and values without having to to-string an instruction and regex (very hacky and never liked it).
3. Refine as_value results building for composites and arrays.
4. Fix eval_insertvalue index retrieval via regex. Seems to be a theme here.