This cross-repository merge unifies the documentation, benchmarks and
code of conduct from the metapackage into Qiskit/Terra's build.
There are very non-trivial merge conflicts that have been resolved by
this commit. The summary is:
- `CODE_OF_CONDUCT.md`: taken directly from the metapackage's version.
- `docs/conf.py`: strongly unified, albeit without the translations
components that are added in a separate commit.
- `docs/index.rst`: taken almost verbatim from the metapackage. All the
API documentation RST files on Terra are moved to `docs/apidoc`
(without the trailing 's') to match the metapackage expectation, so
the URLs of built documentation will not change.
- `docs/release_notes.rst`: The metapackage's version is renamed to
`docs/legacy_release_notes.rst`, given a small introductory header,
and made an orphan linked only from a _new_ `docs/release_notes.rst`
that uses `reno`.
- `docs/tutorials.rst`: Mostly these were the same already. Updated to
include Qiskit/Terra's correction that it's not an orphan, and contain
the metapackage's extra intro tutorial.
- `docs/apidoc/terra.rst`: renamed to `docs/apidoc/index.rst` and retitled
to be correctly just "API Documentation".
- `requirements-dev.txt`: the version of the Sphinx theme is bumped to 1.14
to match the metapackage expectation.
Jake Lishman