Fix RTD rendering of inheritance diagram; show API docs

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (a1c3ebd) 98.24% compared to head (05213f9) 98.24%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #120 +/- ## ======================================= Coverage 98.24% 98.24% ======================================= Files 8 8 Lines 1428 1428 ======================================= Hits 1403 1403 Misses 25 25 ```

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[weiwei]

Wow look what happens during a network glitch

[cmarqu]

Argh, something is still not right. I'll prepare another PR in a few hours.

I'm kinda flying blind because I don't see doc builds for PRs - did you do the settings from #113 in the RTD GUI?