This line isn't necessary.
No need to sign buttons.
Add spec for form builder.
Allow additional fields to be added to the form. Closes #1
Test against Rails.
Get rid of HashWithIndifferentAccess since it does some duping.

I could hack around it but I don't think it is necessary to have indifferent access anyway. It is more important that the references
are maintained.
Add fields_for tests.
Add specs for permit signed attributes.