Documentation restructurization and fixes

[tkornuta-ibm]

Restructured the documentation, fixing errors and warnings

[vmarois]

Nice changes! The documentation looks a bit cleaner.

I have done a few more things:

• Fixed a small warning linked to the installation.rst file,
• Commented out html_static_path in conf.py as we do not have any custom static files to serve yet (e.g. style sheets etc),
• Added an intersphinx link to the matplotlib doc, so we'll be able to link classes like

:py:class:matplotlib.figure.Figure

• Commented out make html in doc_build.sh as we actually do not need this command. readthedocs does not use any make file to build the doc, only the sphinx-build command (you can check the commands used during a build here.
  So I would go even further and delete the file make.bat and Makefile in docs/ as we do not need them. I would also argue that the script used to locally build the doc should mimic as close as possible readthedocs and thus do not rely on make.

These tiny fixes removed the remaining warnings, except for one:

WARNING: Duplicate ID: "module-miprometheus.problems".

I am pretty sure this is caused by problems.rst, as it contains the following directive twice:

.. automodule:: miprometheus.problems

See this post on stackoverflow.

Hence the duplicate warning. Removing the second line causes the build to fail, so we shouldn't. I would leave this warning as is for now.