Add @content annotation

If the annotations was added by hand the `item.content` key will look like:
```js
item.content = [{
  description : '[Description]',
  autogenerated : false 
}]
```

If the annotation was added based on finding the string `@content` inside of `item.context.code` it will look like:
```js
item.content = [{
  autogenerated : true 
}]
```

A annotation written by hand will never be overwritten by an autogenerated one. 

This should Fix #226