Added new opcodes:
OPCODE_CALL
OPCODE_RET
OPCODE_LOAD_THIS
OPCODE_LOAD_NULL
OPCODE_LOAD_ARG

- and started on special opcodes; now only:
OPCODE_SPECIAL_LOG to support console logging

Signed-off-by: Jakob Brandsborg Ehmsen <jakobehmsen.github@gmail.com>