More typo fixes across the tree

Previously I have made spelling changes as caught by Debian's lintian
tool, which has a short list of common misspellings that it tests for.
This time I decided to run codespell against the source and fix all the
obvious problems it came up with. It also uses a list of misspellings
but it's much larger than lintian's, but also has some false positives
so I went over the list by hand.

The command I used to do check the source was:
git ls-tree -rz --name-only HEAD | xargs -0 codespell -L minimise,errorstring

shairport-sync.spec

@@ -79,12 +79,12 @@ getent passwd %{name} &> /dev/null || useradd --system -c "%{name} User" \
 * Thu Dec 21 2017 Mike Brady <mikebrady@eircom.net> 3.1.7
 - Bug fix for unexpectedly resuming play at full volume from iOS 11.2 and macOS 10.3.2.
 * Mon Dec 11 2017 Mike Brady <mikebrady@eircom.net> 3.1.5
-- Bug fixes and better compatability with iOS 11.2 and mac OS 10.13.2.
+- Bug fixes and better compatibility with iOS 11.2 and mac OS 10.13.2.
 - Better AirPlay synchronisation.
 * Wed Sep 13 2017 Bill Peck <bpeck@redhat.com> 3.1.2-1
 - New upstream release
 - The default value for the alsa setting mute_using_playback_switch has
-  been changed to "no" for compatability with other audio players on the
+  been changed to "no" for compatibility with other audio players on the
   same machine. Because of this you may need to unmute your audio device
   if you are upgrading from an older release.
 - Fixed bugs that made Shairport Sync drop out or become unavailable when