The API documentation says "move as much data as possible", and if
there is room at the head of the buffer, we should use that if the
room after the tail is not large enough.

The result shall be positive.

This is the version in Debian Stretch (stable).

MPD has minSdkVersion=21 which is above all the checks here.

Since nfs_stat_async is deprecated.

This is the version in Debian Jessie (oldstable), a reasonable "old
enough" version to keep support for.

add 2 preferences to:
 - enable Wakelock when MPD is running (prevent suspend)
 - run MPD on boot

and display MPD logs

 - <uses-permission> must be before <application>
 - specify allowBackup (default)

- add Settings: Activity to start / stop MPD Service (Main).

- Main is a service that run in foreground with a notification. See
  Service.startForeground documentation for more details.

- Main.Client is used to control the service: start or stop it and also receive
  callbacks when service encounters an error, is killed, is started or is
  stopped.

- Main.start to start the service without any fallback.