First version of the documentation

[HealthyPear]

This PR sets up the first version of the documentation based on Sphinx.

Details about the docs

• added some new dependencies
• the contents reflect mostly what I found already there, since I didn't start using this project seriously
• the stylistic choices like the theme and the structure of the documentation are mostly based on my personal preference, they can be of course changed
• warnings are treated as errors as a conservative choice

Changes to other parts of the package

• added .mailmap file
• the API members have been exposed for Sphinx to find
• the argument parser for the bkgmodel script has been made a global variable for sphinx-argparse
• a small fix where a class attribute was private, but was described as public
• the test coverage job was saying 100%, but it's 1% - the reason was a wrong path given to pytest-cov

Deployment

• the CI has been updated with a job to deploy on GitHub Pages (easy to activate from the repo's settings, but not easy to support multiple versions when the project starts to tag releases)
• there is a configuration file for ReadTheDocs; the project has been created by me here and I tested successfully the build of the documentation of the branch related to this PR, but the repository needs to be connected to the service by an administrator via a webhook in order for commits to automatically trigger the build in the future.

[codecov]

Codecov Report

Patch coverage: 0.29% and project coverage change: -99.71 ⚠️

Comparison is base (22852a7) 100.00% compared to head (cf34cf3) 0.29%.

Additional details and impacted files

@@             Coverage Diff             @@
##              main      #9       +/-   ##
===========================================
- Coverage   100.00%   0.29%   -99.71%     
===========================================
  Files            2       6        +4     
  Lines            3     685      +682     
===========================================
- Hits             3       2        -1     
- Misses           0     683      +683     

Impacted Files	Coverage Δ
src/pybkgmodel/camera.py	0.00% <0.00%> (ø)
src/pybkgmodel/data.py	0.00% <0.00%> (ø)
src/pybkgmodel/message.py	0.00% <0.00%> (ø)
src/pybkgmodel/model.py	0.00% <0.00%> (ø)
src/pybkgmodel/processing.py	0.00% <0.00%> (ø)
src/pybkgmodel/tests/test_basic.py	100.00% <100.00%> (ø)

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.