make it goinstallable with latest goinstall

Go version:
	6g version weekly.2011-10-06 9966
gofix error
fix package description
examples: fix import path
examples: fix build
remove all Makefiles
add an example test

--HG--
rename : examples/status.go => mpd/example_test.go
document example
Add authenticated connection
Fix typo in Previous()
Add SetVolume()
Add GetFiles()

- Addresses code review comments by @fhs, thanks!