Fixes the usage of 'argument' and 'extra' for opcode::doPrimitive

Issue: #32
Moves some code of TSmalltalkInstruction class from headers into .cpp file

Removes TInstruction from types.h.
Adds method TSmalltalkInstruction::toString().

Issue: #32
Builds all graph* and parsed* code into a separate libstapi

Issue: #32
Add stub for tests

Issue: #32
Adds test for TSmalltalkInstruction

Issue: #32
Adds tests for InstructionDecoder

Issue: #32