Tri-form

~~~~~~~~~~~~~~~~~~~

* Datetime fields used to not roundtrip cleanly via the form (they output
milliseconds then failed on parsing them) Field.file didn't exist.

* Changed syntax for specifying html attributes and classes. They are now use
the same way of addressing as other things, e.g.:
Field.choice(attrs__foo="bar", attrs__class__baz=True) will yield something
like `<select ... class="baz" foo=bar>...</select>`

~~~~~~~~~~~~~~~~~~~

* Made sure form validation is only run once

* Fixed input form class and render context to create_or_edit_object view

~~~~~~~~~~~~~~~~~~

* Fixed default value initialization on Field attributes to not reuse containers.

* Added support for ManyToManyField when generating forms for model objects.

* Added 'read_from_instance' and 'write_to_instance' callbacks for customized instance marshalling.

~~~~~~~~~~~~~~~~~~

Bugfix release.

* Added missing 'after' attribute on Field prohibiting form order customization

* Fixed default value handling of 'attr' to make None a valid value when no attribute should be read.

* Fixed CSS handling on required fields.

~~~~~~~~~~~~~~~~~~

* Made evaluation of choices lazy even when there is a None alternative.