video: first signs of life

The video code now writes out a bmp file per-frame. With this patch
applied, the Nintendo logo is rendered in each frame.

There is still plenty of work to be done. Pretty much everything is
hardcoded to make the bootrom work.

src/gbemu/memory.c

@@ -52,6 +52,11 @@ void gb_mem_write(struct gb_memory *cpu, uint16_t addr, uint8_t val)
 	case 0xFF40 ... 0xFF4B:
 		gb_video_mem_write(video, addr, val);
 		break;
+	case 0x8000 ... 0x87FF:
+	case 0x9800 ... 0x9BFF:
+		printf("Wrote [0x%x]=%x\n", addr, val);
+		ram[addr] = val;
+		break;
 	case 0 ... 0x100:
 		if (bootrom_mapped) {
 			break;