HCDFormat: Add docs on ripping cds
hcd: Drop ISO_path, and MP3_path

* Lets handle this a little smarter,
  look in the base directory of the hcd file.
* If users want a custom path for the audio,
  they can specify it in the hcd.
* I've never seen an hcd use ISO_Path or MP3_path
  so I think the impact will be minimal.