Merge branch 'development'

Update Docker images o that additional command line arguments to the docker run command are passed to the shairport-sync application.
(This is the behaviour of the original 3.3.8 docker image but was missing from the AirPlay 2 development version.)
Use the s6-overlay system on the Classic docker image.
Fix a bug that delayed metadata appearing in the D-Bus, MPRIS and MQTT interfaces.
Clean up the generation of Play/Pause/Stop conditions.
Add Pause stage generation for AirPlay Buffered streams.
CLean up some of the documents.

diff --cc docker/classic/README.md
index 09ac88722a917b9775f9db1b31d975d94ba6f14e,9bbf51e6f2981529f1b1551eeaa3facb5aa74d54..abc69b66e5a3fa4bc6b11d02dea9990b3e0889d4
--- 1/docker/classic/README.md
--- 2/docker/classic/README.md
+++ b/docker/classic/README.md
@@@ -1,3 -1,3 +1,3 @@@
- # Classic (AirPlay 1 Only) Docker Image
+ # Classic (aka AirPlay 1 Only) Docker Image
  
 -See the [Shairport Sync Docker Hub Repo](https://hub.docker.com/r/mikebrady/shairport-sync) for available tags.
 +See the [Shairport Sync Docker Hub Repo](https://hub.docker.com/r/mikebrady/shairport-sync) for available tags.