Implemented mod, halt, and jump instructions

creature.go

@@ -91,8 +91,26 @@ func (machine *Machine) Execute (offset int) {
 			machine.Push(notEqual)
 			
 		case 0xc:
+			// MOD
+			// performs a modulo operation of the second to last
+			// word on the stack to the last word on the stack
+			machine.Push(machine.Pop() % machine.Pop())
+			
 		case 0xd:
+			// HALT
+			// stops execution
+			return
+			
 		case 0xe:
+			// JMP
+			// jump to the address specified by the last word on the
+			// stack if the second to last word on the stack is
+			// nonzero
+			jumpTo := machine.Pop()
+			if machine.Pop() != 0 {
+				machine.counter = jumpTo - 1
+			}
+		
 		case 0xf:
 		}
 		machine.counter ++