Add automodsumm_included_members option

[lukelbd]

Implements item 2 from #91. This adds and documents the automodsumm_included_members option, which is used to add private methods other than __init__ and __call__ to the online documentation. This is useful when creating array-like or dict-like classes, for which it would be useful to document special class methods like __setitem__ and __getitem__.

[codecov[bot]]

Codecov Report

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

Project coverage is 87.19%. Comparing base (4c8e33c) to head (8e59794). Report is 141 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #103 +/- ## ======================================= Coverage 87.19% 87.19% ======================================= Files 5 5 Lines 695 695 ======================================= Hits 606 606 Misses 89 89 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[astrofrog]

Looks good, could you rebase this, and add a test? Thanks!

[bsipocz]

This was opened from an org's fork to which maintainers can't push updates. Given the inactivity for the rebase and add test comment above, I'll go ahead and open a separate PR with 1) rebasing the commit from here, 2) cherry-pick and fixup the test from the commit mentioned in the comment above.

[bsipocz]

superseded by #165