Improve autodocs for top-level package names.

[tseaver]

• Drop the __init__ from them.
• Include the ones imported from _implicit_environ'

Fixes#845.

[coveralls]

Coverage remained the same at 100.0% when pulling 22e4c63 on tseaver:845-document__implicit_environ into 9c4867a on GoogleCloudPlatform:master.

[dhermes]

I've checked out this branch and built the docs. All looks good, can you fix the docstring for datastore.set_defaults so the bullets render correctly? Use * instead of - for Sphinx.

[dhermes]

Also a concern, this is very manual. How will we make sure new methods in __init__ get added to the docs?

[tseaver]

fbba1c4 fixes the bullet rendering (not *, but a leading blank line, was required).

WRT manual config: We can't have best of all worlds for members imported into the base package:

• Adding :imported-members: would pick up all the imports.
• Adding just the ones we want to __all__ would make using the others look unsupported.

The real fix would be to move those implementations into the base package, and have them just tweak the defaults object in _implicit_environ.

[coveralls]

Coverage remained the same at 100.0% when pulling fbba1c4 on tseaver:845-document__implicit_environ into 9c4867a on GoogleCloudPlatform:master.

[dhermes]

I don't think the circular import gymnastics is worth it for this somewhat minor nit. Proceed: LGTM.