barriers & registers tracking for sass disasm

Finally I add registers tracking in my perl sass disasm

Now I can do some full-featured analysis of sass - like find candidates pairs of instruction to swap/run them in so called "dual" mode - and all of this in barely 1200 LoC of perl code

Let's think what must mean for couple of instructions to be fully independent:

1. they should belong to the same block - like in case of
     IADD R8, -R3, RZ
.L_x_14:
  FMUL R11, R3.reuse, R3 instructions should be treated as located in different blocks
2. they should not depend from the same barriers
3. they should not update registers used by each other 

So I implemented building of code-flow graph, barriers & registers tracking

Building of CFG