Created 16-bit addition base class.
Fixed more bit shifting logic. Java is annoying sometimes.
Added a few 16 bit tests
More addition opcodes completed. One more to go
Corrected a switch statment fall-through that shouldn't
Filled out more addition opcode tests
Added IOpcodeMap interface
Removed opcode initialization code from GameBoyProcessor and placed in Opcodes, which now implements IOpcodeMap
Added shell of final Add instruction. Implementation to follow.