Issue #13 -  Get parts of content independently

New feature added as @bradvogel suggested in #13:

```javascript
var extractor = require('unfluff');
var everything = extractor(html);
var justTitle = extractor.title(html);
```
Late thought about this code. Maybe we can use properties created by Object.defineProperty instead of bare methods to have same object interface for unfluff.lazy result? Usage will be like:

```javascript
var unfluff = require('unfluff');
var doc = unfluff.lazy(html);
console.log(doc.title);
```

What do you think?