[suggestion] use a sub-command style of command-line interface

[tstack]

I'd like to suggest making the command interface use sub-commands for some added ease-of-use and clarity. Right now, just typing litho will start the sync process. That's a heavyweight operation that a new user might be surprised by when they were just trying to figure out what the command does. A sub-command interface would also keep the door open for adding other operations, like logging out.

$ litho
<prints help>
$ litho sync
...