implement new command: cowsay

[jiacai2050]

$ cowsay hi
 ____ 
< hi >
 ---- 
        \   ^__^
         \  (oo)\_______
            (__)\       )\/\
                ||----w |
                ||     ||

$ cowsay -f tux hi
 ____ 
< hi >
 ---- 
   \
    \
        .--.
       |o_o |
       |:_/ |
      //   \ \
     (|     | )
    /'\_   _/`\
    \___)=(___/

• https://en.wikipedia.org/wiki/Cowsay