title: Pass options containing spaces to ffmpeg using fluent-ffmpeg
body: <p>I am writing a Node script which copies and re-tags some of my MP4 files using <code>fluent-ffmpeg</code></p>
  
  <p>It doesn't work with any metadata that contains spaces. The code that does the copying/tagging looks something like this:</p>
  
  <pre><code>const ffmpeg = require('fluent-ffmpeg');
  
  const inputFilename = 'path/to/original.m4a';
  const outputFilename = 'path/to/new.m4a';
  
  const options = [
      '-metadata', 'artist=Someone',
      '-metadata', 'album=Some title',
      // ...etc
  ];
  
  ffmpeg(inputFilename)
    .outputOptions(options)
    .saveToFile(outputFilename);
  </code></pre>
  
  <p>This results in an error:</p>
  
  <pre><code>events.js:183
        throw er; // Unhandled 'error' event
  
  An error occurred: ffmpeg exited with code 1: title: Invalid argument
  </code></pre>
  
  <p>I have tried putting <code>Some title</code> in single quotes, double quotes and no quotes. I have tried escaping the spaces in it. I have tried passing the options array as single options rather than tuples, for example: <code>'-metadata album="Some title"'</code> - but whatever I try, it still throws an error when there are spaces.</p>
  
  <p>(It may be relevant to note that this is on Windows)</p>
  
  <p>Can anyone suggest a way of getting it to work?</p>