[builder] Make sure that unparent_wheel is automatically called
[doc] Add a tag for moos
[doc] Rewrite new_middleware

- explicit how to add datastream handler in the class based method
- Provide specific explanation for each middleware, with various
  examples
- document how to add a datastream manager

XXX: maybe we must split it in two ?
XXX: write MOOS specific stuff when it is ready. See #275

Still, it fixes #281