Optimization: construct refregs array once

Testing the avradd code (which still crashes at some point)
Performance improved approximately by 8% on my pc in a release build with
dmd and the printlines in the simulator disabled.
Optimization: Optimized jumps to jumpIndex

Same configuration as my previous commit, simulation runs 4.75 times faster on my pc
Optimization: Prevent vtbl lookups in setBit

Verified removal of vtbl by inspecting the llvm code. Compiled with ldc flags
-O5 -release -output-ll and then llvm-link **/*.ll | opt -std-compile-opts |
llvm-dis
12% speed improvement using llc with -release and -O5
Unittests compile (were broken since refactoring)
Optimization: Memory class directly references mem

25% speed improvement via llvm