[Feature] Support creating an El Torito (CD-ROM) bootable image

[michalusio]

Hi!
First off, I wanted to thank the creator and the contributors of this package for all the great work.

Now, onto the issue:
I have been using the bootloader to run a small kernel I'm writing and I have noticed that while I can boot when the built image is attached as a hard drive to QEMU, I am not able to boot when it's attached as a CD-ROM.
I have dug deeper and from what I've read it is because CD-ROMs have a completely separate booting system called El Torito.

As such, I would like to know if there would be a possibility of adding El Torito support and add it so we could build the images directly for booting from a CD?

[phil-opp]

I don't know much about the El Torito format, but I don't see any problems with adding support for it. I personally don't have the time to do it, but I'd be happy to merge a PR. I recommend to wait until #232 is merged though, as it should make the implementation simpler.