add tts-server executable

This makes the project easier to use when installing via package manager.

server/server.py

@@ -76,5 +76,9 @@ def tts():
     return send_file(data, mimetype='audio/wav')
 
 
-if __name__ == '__main__':
+def main():
     app.run(debug=args.debug, host='0.0.0.0', port=args.port)
+
+
+if __name__ == '__main__':
+    main()