title: commander.js: fails trying to use a parameter named "options"
body: <p>I'm trying out commander.js for parsing arguments in my command-line tool, but it doesn't work properly when I use a parameter named <code>--options</code>:</p>
  
  <pre><code>// two params, both are optional
  program
    .option('--api &lt;apiYaml&gt;')
    .option('--options &lt;optionsYaml&gt;')
    .parse(process.argv);
  
  if (program.options) {
    let optionsFile = path.resolve(program.options);
    ...
  
  if (program.api) {
    let apiFile = path.resolve(program.api);
    ...
  </code></pre>
  
  <p>This code works fine for the --api parameter, but dies when I call without an  --options parameter.</p>
  
  <p>Adding some debug and looking at the <code>program</code> object, I see that the problem is that <code>program</code> already has an <code>options</code> property, as well as properties named <code>args</code>, <code>commands</code>, and <code>rawArgs</code>. Does that mean it's impossible to use any of those strings as parameters to my program, or is there a workaround? Is this documented anywhere?</p>