- Allow prefix on Xref converter
- Add option to include module name in messages. Incoming and outgoing message value have the same comportment.
  For example, if __converter__ is used as the module, both generated messages and received message will contain __converter__.<name>.
  Previously, generated messages would use the module name while received one would not.

In Model converter, also validate messages in ``message_to_odoo``.

Model converter argument changed, `__type__` is now the last argument and is optional. It is expected not to be used
anymore.
Added possible_datatypes property and odoo_datatype on Converter. Defaults to empty set and None.
On Model, it can be set.

Replace generic exceptions.

 Add some typing information, or make it consistent.
 Add more docstrings.
 Fix using Skip in switch converter.

to facilitate expression error handling

 Use ©

Used by other modules; these exports got removed when I replaced an ``import *`` earlier.