Integrate with Phoenix Forms

[Adzz]

We should investigate how best to do this or if this is desireable / possible. Seems like we would have to implement something that implements the Phoenix.HTML.FormData protocol perhaps. Effectively very similar to changesets at that point.

We should also think if this is to be used as a form validation layer how would it integrate to ecto further into the stack. Could look here for inspiration: https://github.com/phoenixframework/phoenix_ecto/blob/master/lib/phoenix_ecto/html.ex

[Adzz]

TODO

1. implement a minimal repro where we implement HTML.FormData for a struct and get it working.