Spin a spinner while tmux sessions are restored

Closes #16

scripts/tmux_spinner.sh

@@ -0,0 +1,29 @@
+#!/usr/bin/env bash
+
+# This script shows tmux spinner with a message. It is intended to be running
+# as a background process which should be `kill`ed at the end.
+#
+# Example usage:
+#
+#   ./tmux_spinner.sh "Working..." "End message!" &
+#   SPINNER_PID=$!
+#   ..
+#   .. execute commands here
+#   ..
+#   kill $SPINNER_PID # Stops spinner and displays 'End message!'
+
+MESSAGE="$1"
+END_MESSAGE="$2"
+SPIN='-\|/'
+
+trap "tmux display-message $END_MESSAGE; exit" SIGINT SIGTERM
+
+main() {
+	local i=0
+	while true; do
+	  i=$(( (i+1) %4 ))
+	  tmux display-message " ${SPIN:$i:1} $MESSAGE"
+	  sleep 0.1
+	done
+}
+main