Token module (Pathauto 5.x-2.x) support

I wanted to use pathauto to generate aliases for audionodes by album name. I could have set up a taxonomy term for each album, but that seemed silly since the information was already in the ID3. So, after a bit of hacking around, I implemented the pathauto_node hook myself.

I've created pathauto placeholders for track number, title, album, artist, year, and genre. I'm only using album, but I did test that all of them at least work. One thing that someone might want to fix - it really should add a leading zero to the track number if it's only one digit.

I'm not that knowledgeable about PHP, so this code might not be bulletproof or efficient. I also don't have shell access to run diff on my web server, so this is just a cut-and-paste of the function itself and not a patch. But at least it'll give someone a starting point.