Support for inline forms

Howdy

This PR adds basic support for inline form labels.

Usage:

```ruby
form_for(@article, inline: true) do |f|
  f.text_field :title
  f.text_field :something
  f.submit
end
```

Which will look like this:
![23 02 13_20_51-Bildschirmkopie](https://f.cloud.github.com/assets/480921/188517/7ddf5eea-7df2-11e2-85c6-892e47646000.png)