feat: implement ability to boot straigt to cartridge

src/main.rs

@@ -3,13 +3,15 @@ use gb::cpu::Cpu as LR35902;
 fn main() {
     let mut game_boy = LR35902::new();
 
+    game_boy.load_cartridge("bin/cpu_instrs.gb");
+
     loop {
         let pc = game_boy.register_pair(gb::cpu::RegisterPair::PC);
         let opcode = game_boy.fetch();
         let instruction = game_boy.decode(opcode);
 
         println!(
-            "Addr: {:#06x} | Opcode: {:#x} | Instr: {:x?}",
+            "Addr: {:#06X} | Opcode: {:#04X} | Instr: {:X?}",
             pc, opcode, instruction
         );