RFE: Support some command line switches, especially -h / --help

[siebenmann]

Right now rink takes all command line argument(s) as a file to load, and it doesn't deal very well if the file isn't there, perhaps because you innocently tried to use -h to see if there was any command line usage help:

$ rink -h
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Error { repr: Os { code: 2, message: "No such file or directory" } }', src/libcore/result.rs:906:4
note: Run with `RUST_BACKTRACE=1` for a backtrace.

It would be nice if rink supported -h / --help, and also perhaps --version, especially if one or the other reported the URL of the repository (so I could remember to check it every so often for new versions).