DOC: Get rid of API doc warnings

[pllim]

I disabled "fail on warnings" for RTD in #58. If you want to enable it again, you have to fix the warnings. The CI had not run for 7 months before I touched it so no idea what happened and I don't have time to follow up on this.

reftools/getphotpars.py:docstring of reftools.getphotpars.GetPhotPars:40: WARNING: autosummary: stub file not found 'reftools.getphotpars.GetPhotPars.close'. Check your autosummary_generate setting.
reftools/getphotpars.py:docstring of reftools.getphotpars.GetPhotPars:40: WARNING: autosummary: stub file not found 'reftools.getphotpars.GetPhotPars.get_phot_pars'. Check your autosummary_generate setting.
reftools/imphtcomp.py:docstring of reftools.imphtcomp.ImphttabComp:68: WARNING: autosummary: stub file not found 'reftools.imphtcomp.ImphttabComp.make_plot'. Check your autosummary_generate setting.
reftools/imphtcomp.py:docstring of reftools.imphtcomp.ImphttabComp:68: WARNING: autosummary: stub file not found 'reftools.imphtcomp.ImphttabComp.print_diffs'. Check your autosummary_generate setting.
reftools/interpretdq.py:docstring of reftools.interpretdq.DQParser:55: WARNING: autosummary: stub file not found 'reftools.interpretdq.DQParser.from_instrument'. Check your autosummary_generate setting.
reftools/interpretdq.py:docstring of reftools.interpretdq.DQParser:55: WARNING: autosummary: stub file not found 'reftools.interpretdq.DQParser.interpret_array'. Check your autosummary_generate setting.
reftools/interpretdq.py:docstring of reftools.interpretdq.DQParser:55: WARNING: autosummary: stub file not found 'reftools.interpretdq.DQParser.interpret_dqval'. Check your autosummary_generate setting.
reftools/interpretdq.py:docstring of reftools.interpretdq.ImageDQ:38: WARNING: autosummary: stub file not found 'reftools.interpretdq.ImageDQ.dq_mask'. Check your autosummary_generate setting.
reftools/interpretdq.py:docstring of reftools.interpretdq.ImageDQ:38: WARNING: autosummary: stub file not found 'reftools.interpretdq.ImageDQ.from_fits'. Check your autosummary_generate setting.
reftools/interpretdq.py:docstring of reftools.interpretdq.ImageDQ:38: WARNING: autosummary: stub file not found 'reftools.interpretdq.ImageDQ.interpret_all'. Check your autosummary_generate setting.
reftools/interpretdq.py:docstring of reftools.interpretdq.ImageDQ:38: WARNING: autosummary: stub file not found 'reftools.interpretdq.ImageDQ.interpret_pixel'. Check your autosummary_generate setting.
reftools/interpretdq.py:docstring of reftools.interpretdq.ImageDQ:38: WARNING: autosummary: stub file not found 'reftools.interpretdq.ImageDQ.pixlist'. Check your autosummary_generate setting.