Use h2 instead of label for option headers
Extract valid options to class method

This reduces the number of places that need to change when adding new
options.
Remove hyphen
Require all files in option_renderer/ directory

This makes it so we can add more renderers without having to change this
file and `.for` will still work.
Add test for OptionRenderer.for
Rename `OptionRenderer.for` to `OptionRenderer.renderer_for`

This should be a little clearer
Add `OptionRenderer.render` for convenience

`OptionRenderer.render(option, value)` looks much better than:
`OptionRenderer.renderer_for(option).new(value).render`
Remove protected attribute from params

This was failing because the attributes were restricted and foo was not a valid
key. Not sure how this passed before but this should fix it.
Use double to avoid loading Rails model
Refactor option renderers for clarity

Mostly style changes
Add backspace option