Maintenance release with some development.

Bug fixes, stability improvements on poor networks.
Buffering and flushing works somewhat better, though still not bulletproof.
Work is in progress on being able to quickly stop using the ALSA sound device to enable other sound apps to use it:

• Pausing immediately closes the ALSA device, playing tries to open it and use it.
• Sending a SIGUSR2 to shairport-sync will cause it to send a pause request to the client. If the client is iTunes, it will immediately pause.
• If shairport-sync has been properly daemonised (with shairport-sync -d....) then shairport-sync -P will run another copy of shairport-sync which will send a SIGUSR2 to the shairport-sync daemon and then exit, causing the daemon to ask the client for a pause. The copy of shairport-sync might need to have root privileges.