Form Helper

This is a WIP spike, please feel free to comment or suggest changes. An end goal for
me to is have something like
[SimpleForm](https://github.com/plataformatec/simple_form/) so hopefully
@josevalim will have some thoughts.

This will also rely heavily on the `Resource` protocol discussed in #320.
I don't know of a better place for this (yet) due to the fact that it's not only used for forms. If you have a link, `method: :delete` will become `data-method="delete" rel="nofollow"` but for a form it should just be `method="delete"`