sphinx_build breaks with sphinx > 2.x

[jameshiebert]

I just tried to build the docs on my workstation, which seems to not be working.

(ce-venv) james@basalt:~/code/git/climate-explorer-backend$ python setup.py build_sphinx
running build_sphinx
Running Sphinx v3.0.2

Exception occurred:
  File "/tmp/ce-venv/lib/python3.6/site-packages/sphinx/application.py", line 1069, in add_source_parser
    self.registry.add_source_parser(*args, **kwargs)
TypeError: add_source_parser() takes 2 positional arguments but 3 were given
The full traceback has been saved in /tmp/sphinx-err-9aso6dr3.log, if you want to report the issue to the developers.
Please also report this if it was a user error, so that a better error message can be provided next time.
A bug report can be filed in the tracker at <https://github.com/sphinx-doc/sphinx/issues>. Thanks!

After downgrading Sphinx to 2.4.4 the build works, but we can see a deprecation warning that we have apparently been ignoring:

(ce-venv) james@basalt:~/code/git/climate-explorer-backend$ python setup.py build_sphinx
running build_sphinx
Running Sphinx v2.4.4
/tmp/ce-venv/lib/python3.6/site-packages/m2r.py:652: RemovedInSphinx30Warning: app.add_source_parser() does not support suffix argument. Use app.add_source_suffix() instead.
  app.add_source_parser('.md', M2RParser)
...

I'm not sure where the Markdown parser is configured, so I'm not sure where to point anyone for the solution. @rod-glover , you set this up didn't you?

[corviday]

I set sphinx up in this repository in December as part of the MOTI project, since documenting the API was part of the remit, but its configuration is not adequately robust and it does not behave as expected when built under different conditions: 1, 2. Definitely some more work needed.

We're using the m2r sphinx extension to parse *.md files into *.rst files for sphinx. We haven't pinned m2r, so you presumably have the latest version of m2r on your workstation. m2r may itself need an update, or perhaps there's a different sphinx markdown extension we should use.