Upgrade from 0.1 to 0.2

## TL;DR

• Rename changeset_after_create_callback to modify_changeset

• Move your validation rules from changeset_validation to modify_changeset

  ## Full story

  After extracting ecto related code from main formex library to formex_ecto errors from changeset wasn’t used anymore. This library introduced Formex.Changeset.Validator that let us use validation functions included in Ecto.Changeset module. This module creates a fake changeset to perform validation.

  In previous version formex_ecto was raising error if there was an error in changeset after insert/update failure. This error was introduced because we should use new callback changeset_validation instead of changeset_after_create_callback.

  There is one issue with this approach - Ecto can also add an error to changeset on it’s own. For example - if there is an UNIQUE constraint then Ecto will attach error to the changeset after failure of database query. So formex_ecto was raising error even though programmer didn’t make a mistake with callbacks.

  From now instead of raising error, all errors from changeset are passed back to the form and displayed for user. Just like in the formex before 0.5 version.

  Another change is renaming a long changeset_after_create_callback to a shorter modify_changeset. This update was a good occasion to do that. When I first introduced this callback I thought there will be need for to make much more similar callbacks (like in Symfony & Doctrine) but no one asked for them yet.

  The changeset_validation callback is removed. You should move validation rules to the modify_changeset. If you are using validation attached to field (add(:name, :text_input, validation: [ __some changeset's rules__ ])) you don’t need to change it. They are still performed on a fake changeset mentioned before.