Take CLI options in standard way

It now can take `-H`/`--host` and `-p`/`--port` options, and also provide `--help` message.  I prefer `optparse` (which was deprecated since Python 2.7) over `argparse` (which was introduced from Python 2.7) here because of Python 2.6 compatibility.  Feel free to change it to `argparse` if you don’t mind under Python 2.7.