Patch 3: Make default callbacks simpler.

I want to move as much to a 1 file/1 value model as possible. I haven't
come up with a clean way to enforce it except via social pressure.

This patch is a step in that direction. It:

- Reduces the output of 'power' to just the decimal state of the device
- Adds a 'name' file which exports just the device name
- Reduces the 'status' file to just export the bus ID. (This will change,
  since the bus ID is obvious based on what directory you're in, but it's
  another patch at another time)