Add .save command, addresses issue #20

[skypanther]

I originally wrote this to write to the user's home directory by default. Hence the getUserHome() function. In the end, it writes to just the current directory. I can remove that function, or update the logic to write to the user's home dir. Lemme know.

[tonylukasavage]

I resolved this differently. There's no reason to maintain a history since the readline Interface already maintains one. I'd be happy to take the doc update though by itself if you wanted to push another one.