Add MQTT documentation and associated README update. Fix bug cuasing hang if an on...

diff --cc README.md
Simple merge

diff --cc configure.ac
index d745ac718eb9a0eb33b4883d29bff0a109ee68cd,adedf3fea218f7f79a75b00a3ff11cf419ebbdf1..8954916eb3e97d3fe3dbdae81b55df15309dbb78
--- 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], [3.3.8rc1], [4265913+mikebrady@users.noreply.github.com])
 -AC_INIT([shairport-sync], [3.3.8d3], [4265913+mikebrady@users.noreply.github.com])
++AC_INIT([shairport-sync], [3.3.8rc2], [4265913+mikebrady@users.noreply.github.com])
  AM_INIT_AUTOMAKE
  AC_CONFIG_SRCDIR([shairport.c])
  AC_CONFIG_HEADERS([config.h])