Use uva-node commands directly from command line

Add the ability for uva-node commands to be called directly from the command line, by specifying them as arguments to uva-node. For example, instead of doing:

    $ node index.js
    > edit test.cpp
    > send 123 test.cpp
    > stat

One could instead do:

    $ node index.js edit test.cpp
    $ node index.js send 123 test.cpp
    $ node index.js stat

This allows the user to do other stuff on the command line in between commands, without having another terminal open or having to quit and reopen uva-node. This also allows the user to create his own command line aliases, and supports auto-completion of filenames.