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.
This test: `assert tag(:input, data: [toggle: [target: "#parent"]]) == "<input data-toggle-target=\"#parent\">"` is testing `dasherize` works by nature of the nested data attribute.