Improve layout of per-class documentation

[bkeryan]

Tech Debt

From #151 (comment):

Currently, we generate one class per page and the bintime and waveform classes have detailed documentation in the class docstring. This is almost what I want, except:

1. The constructor signature(s) is at the top, followed by the detailed documentation, then the rest of the class members.
2. The parameters for the constructor are not documented like other methods.

Some ideas on how to improve the layout:

• Go back to one module per page and split nitypes.waveform into submodules (nitypes.waveform.analog, etc.). Note that this breaks compatibility unless we continue to alias the classes into nitypes.waveform, in which case we would need to use the autoapi-skip-member callback to control which copy of the class is documented.
• Set autoapi_add_toctree_entry=False and create separate .rst files that use .. autoapimodule::, .. autoapiclass::, etc. I think this will give us control of the page before/after the class documentation.
• Create a custom autoapi template.
• Switch to autodoc.

AB#3202297