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);
```
I think that would work too, but I don't have a problem with the methods we have now. I'm a little uneasy with properties that cause a significant amount of code to be run when you access them.

However, I'm open to other opinions if anyone feels really strongly about this.