A small function refactor where we centralize things around the cpu.
Also, now it is easier to create more instructions (for SC and OX) and link the decoded instruction with the correct emulated function.
Complete Chip-8 instructions. However, the user still needs to modify the code to select the ROM. Next-step will be to insert SUPER-CHIP and OX-CHIP instructions, as well as to give menu options to the user.