doctest: minor PEP8 adjustments
env: minor comment clarification
autodoc: minor PEP8 adjustments
Change extension setup() return value to a dictionary of metadata.

This makes it possible to introduce more metadata values later.
Move status_iterator to application object.
[WIP] parallel read

--HG--
extra : amend_source : 0e40e40d0d2551bf2c1bac6a6fdcf5634fb24064