Use a more singletonish approach to the form registry
Make the element name available to the element instance
Require full Rails as it is required by simple_form anyways
Move test gemfiles into /test/gemfiles
Don't allow users to change the elements list
Add shortcut elements for simple_form's input and input_field
Allow to create elements without any additional arguments
Allow to conditionally render input and input_field
Explicitly require the delegate module