pulse2jack: Add the option to use a user-selected config file

The pulse configuration file is selected from, in order:
- An environment variable
  - CADENCE_PULSE2JACK_PLAY/CADENCE_PULSE2JACK_PLAYREC
- A file
  - ~/.config/Cadence/pulse2jack/play[+rec].pa
- The original default file
  - $INSTALL_PREFIX/share/cadence/pulse2jack/play[+rec].pa

This is a partial solution for #234

data/cadence-pulse2jack

@@ -68,11 +68,23 @@ exit
 
     -p|--p|--play)
 PLAY_ONLY="yes"
-FILE=$INSTALL_PREFIX/share/cadence/pulse2jack/play.pa
+if test -n "${CADENCE_PULSE2JACK_PLAY}"; then
+	FILE="$CADENCE_PULSE2JACK_PLAY"
+elif test -f ~/.config/Cadence/pulse2jack/play.pa; then
+	FILE=~/.config/Cadence/pulse2jack/play.pa
+else
+	FILE=$INSTALL_PREFIX/share/cadence/pulse2jack/play.pa
+fi
     ;;
 
     *)
-FILE=$INSTALL_PREFIX/share/cadence/pulse2jack/play+rec.pa
+if test -n "${CADENCE_PULSE2JACK_PLAYREC}"; then
+	FILE="$CADENCE_PULSE2JACK_PLAYREC"
+elif test -f ~/.config/Cadence/pulse2jack/play+rec.pa; then
+	FILE=~/.config/Cadence/pulse2jack/play+rec.pa
+else
+	FILE=$INSTALL_PREFIX/share/cadence/pulse2jack/play+rec.pa
+fi
     ;;
 esac