Merge updates from the development branch into the master branch as 4.2.1

diff --cc README.md
index 4a2e068eec547d564c030b1348482f5120fdc9f4,37992583b3e064f3e850baa8c540dd9335358863..7e4ed475de6765552d94eb8f092e0d4dee41ddc8
--- 1/README.md
--- 2/README.md
+++ b/README.md
@@@ -13,7 -13,8 +13,8 @@@ Shairport Sync does not support AirPla
  * Next Steps and Advanced Topics are [here](ADVANCED%20TOPICS/README.md).
  * Runtime settings are documented [here](scripts/shairport-sync.conf).
  * Build configuration options are detailed in [CONFIGURATION FLAGS.md](CONFIGURATION%20FLAGS.md).
 -* The `man` page, detailing command line options, is [here](https://htmlpreview.github.io/?https://github.com/mikebrady/shairport-sync/blob/development/man/shairport-sync.html).
 +* The `man` page, detailing command line options, is [here](https://htmlpreview.github.io/?https://github.com/mikebrady/shairport-sync/blob/master/man/shairport-sync.html).
+ * Some advanced topics and developed in [ADVANCED TOPICS](https://github.com/mikebrady/shairport-sync/tree/master/ADVANCED%20TOPICS).
  
  # Features
  * Outputs AirPlay audio to [ALSA](https://www.alsa-project.org/wiki/Main_Page), [sndio](http://www.sndio.org), [PulseAudio](https://www.freedesktop.org/wiki/Software/PulseAudio/), [Jack Audio](http://jackaudio.org), to a unix pipe or to `STDOUT`. It also has experimental support for [PipeWire](https://pipewire.org) and limited support for [libao](https://xiph.org/ao/) and for [libsoundio](http://libsound.io).

diff --cc configure.ac
index 7797c074bd46c237ebc92024851a18e5520c8935,743b4743804bf5e2e316931f6982ebbb0a895a7e..4f38634bd2ad75d2885a1e41dd7a7e015912b295
--- 1/configure.ac
--- 2/configure.ac
+++ b/configure.ac
@@@ -2,7 -2,7 +2,7 @@@
  # Process this file with autoconf to produce a configure script.
  
  AC_PREREQ([2.50])
- AC_INIT([shairport-sync], [4.2], [4265913+mikebrady@users.noreply.github.com])
 -AC_INIT([shairport-sync], [4.2.1-dev], [4265913+mikebrady@users.noreply.github.com])
++AC_INIT([shairport-sync], [4.2.1], [4265913+mikebrady@users.noreply.github.com])
  AM_INIT_AUTOMAKE([subdir-objects])
  AC_CONFIG_SRCDIR([shairport.c])
  AC_CONFIG_HEADERS([config.h])