Add OP_LOADNIL, OP_ADDI
original commit by miura1729
https://github.com/miura1729/mruby/commit/6445ce84cb15e1a702c2f84c32377cb78b73b9eb
Not escape when conflict block
original commit by miura1729
https://github.com/miura1729/mruby/commit/09200ca5a3ddf99e7811af13f1fc07ba10d018e0