Improve command line parsing

[kjvalencik]

Implements #3

Current Neon's usage:

cargo-cp-artifact $npm_package_json=cdylib=index.node -- cargo build --message-format=json-render-diagnostics

After changes:

cargo-cp-artifact -nc index.node -- cargo build --message-format=json-render-diagnostics

[dherman]

Looks very nice, it's so simple I don't really have any suggestions for the code. Just a question about the brackets around command-line arguments in the help screens.