remove automatic delegation for Form->Fields in favour of explicit forwarding.
change Form.new to only accept one attribute: the composition. we no longer provide support for a separate Representer instance as this showed to be clumsy. override Form::representer_class if you wanna inject your own.
Form::DSL now only creates the composition for us.
Form now provides ::property and ::properties and delegates them to the representer_class.
by making DSL optional, this push lets you define the form properties within the form but allows passing in a single composition object. you don't have to use :on anymore if you composition provides the appropriate API.
adding Form#to_hash and #from_hash, which used to be called #update_with to make forms (almost) nestable.
add tests for nested forms.
add validation for nested forms.