Optimize VM code complication

[nahkd123]

Our VM code compiler can compiles to instructions to save a bit of memory, but further optimizations can be applied to make VM an attractive option for calling eval() repeatedly.

Our VM implementation is based on stack machine, so it should be easy to optimize arithmetic operations for constants. Something like this:

Original code for 12.5 + (23.5 * 18):
  push 12.5
  push 23.5
  push 18
  multiply
  add

Optimized code (first pass):
  push 12.5
  push 423 // push 23.5; push 18; multiply
  add

Optimized code (second pass):
  push 435.5

Optimized code (third pass):
  push 435.5

Because nothing is changed in the code in this pass, no further optimization will be applied.