title: how can I trans this {'person': {'name': 'cc', 'age': 12} } to {'person.name': 'cc', 'person.age': 12}?
body: <p>like this, I have a object:</p>
  
  <pre><code>{
    'person': {
      'like': {
        'color': 'red',
        'food': 'rice'
      },
      'name': {
        'first': {
          'word': 'bob',
          'num': 4
        }
      },
      'age': {
        'next': 18,
        'now': 19
      }
    }
  }
  </code></pre>
  
  <p>I want to trans it to this:  </p>
  
  <pre><code>{
   'person.like.color': 'red',
   'person.like.food': 'rice',
   'name.first.word': 'bob',
   'name.first.num':4,
   ....
  }  
  </code></pre>
  
  <p>how can I trans it? 
  this is three nest, If I have five nest or more? how can I do this?</p>