Make MPD server more like MPD.

Make the search command a substring match instead of exact and support searching for the "any" tag type.

I am looking at replacing mpd with something easier to hack on and this project is next up for testing. Hopefully my workflow is weird enough that I find some more issues for you.

PS: First time with node and first time pushing to open source so don't hesitate to tell me if I am doing it wrong or there is a better way.