Add sphinx configuration

[dweindl]

Add some basic sphinx configuration and make docstrings sphinx-compatible.

cd doc && make html && xdg-open _build/html/index.html

Related to #7

[codecov-commenter]

Codecov Report

Merging #57 (ab71771) into develop (bb36956) will decrease coverage by 0.05%. The diff coverage is 62.50%.

@@             Coverage Diff             @@
##           develop      #57      +/-   ##
===========================================
- Coverage    60.52%   60.48%   -0.05%     
===========================================
  Files           14       14              
  Lines         1510     1516       +6     
===========================================
+ Hits           914      917       +3     
- Misses         596      599       +3     

Files	Coverage Δ
petab_select/candidate_space.py	51.85% <ø> (ø)
petab_select/constants.py	100.00% <100.00%> (ø)
petab_select/criteria.py	38.09% <100.00%> (+0.99%)	:arrow_up:
petab_select/model_subspace.py	80.62% <100.00%> (+0.06%)	:arrow_up:
petab_select/ui.py	24.69% <ø> (ø)
petab_select/model.py	67.45% <0.00%> (-0.41%)	:arrow_down:
petab_select/model_space.py	65.95% <0.00%> (-0.71%)	:arrow_down:
petab_select/problem.py	26.38% <50.00%> (+0.67%)	:arrow_up:

[dweindl]

@dilpath : This allows generating basic API documentation. More fixes and readthedocs configuration in #63. You decide whether you want to merge this, or prettify the documentation first. Or whether I should split it into separate PRs for sphinx-config and docstrings.

[dilpath]

@dilpath : This allows generating basic API documentation. More fixes and readthedocs configuration in #63. You decide whether you want to merge this, or prettify the documentation first. Or whether I should split it into separate PRs for sphinx-config and docstrings.

Sounds good :+1: I'll merge this already since it passes the non-RTD tests.