related to T1330

used by the swh-docs to generate images and schemas when building the
whole documentation.

to prevent sphinx from complaining about these not being included.

to the benefit of MultiHash api

Summary: to make sphinx happy.

Test Plan: make -C docs

Reviewers: ardumont

Reviewed By: ardumont

Differential Revision: https://forge.softwareheritage.org/D571

double back-quote (``) are not interpreted when inside a emphasis block.

This prevent from requiring a too much recent tox version to fire the
tests, especially this allows to run tests using stretch's tox version.

Promote "Resolution" to a new top-level section, because it's now rather
voluminous.

As part of this document the resolver limitations of identifiers.org, that get
in the way of PID contextual information.

Closes T1015
Closes T1223

so pytest does not think they are test classes.

to clear deprecation warnings.