Update manual to "new" audioctl:

Update manual to "new" audioctl:
- stress that its purpose is to set and get variables, it isn't
  a configuration tool (there's nothing to configure anymore)
- document all audio driver variables
- document the difference between /dev/audioctl0 and /dev/audio0
- give an example of how to test hardware capabilities with
  audioctl

ok semarie@, with help from jmc@, fix from Michael W. Bombardieri