Allow the user to pass in a string instead of an array, and let optimist parse it into an array.

I wrote a little expression to parse a string the way it would be parsed into process.argv from the command line. I needed this for a project but this felt like a feature that would be nice for optimist to have itself.

Now you can simply do:

    var result = require('optimist')('-abc -m "some message" --verbose hello there!).argv;
    console.log(result);

and get back the expected result

    { _: ['hello', 'there!'],
  '$0': 'cwd\app.js',
  a: true,
  b: true,
  c: true,
  m: 'some message',
  verbose: true }