Silent errors / warnings occur when building docs

Start with the verbose docs-build commands in tox.ini, then inspect the generated class.rst files and the nitclk directives that set py:currentmodule. Correct the module and method references described in the issue, and investigate the unresolved attribute warnings. Run tox -e clean, tox -e codegen, and tox -e docs; done means the documented viewcode, method, and attribute warnings are addressed.

Description of issue

When building the docs, there are errors and warnings that only show up if passing the verbose (-v) argument to sphinxbuild.

1. viewcode import errors
   We get errors like

ModuleNotFoundError: No module named 'niscope.Session'
viewcode can't import niscope.Session, failed with error "No module named 'niscope.Session'"

This is because we are incorrectly setting .. py:currentmodule:: ${module_name}.Session in class.rst. Session is a class, not a module.
It should be .. py:currentmodule:: ${module_name}.session.

In nitclk, we are sometimes incorrectly setting .. py:currentmodule:: ${module_name}. This needs .session appended to it.
Other times, we are setting .. py:currentmodule:: ${module_name}.SessionReference, which needs SessionReference to become session.

After fixing this, other problems are revealed.

2. Methods aren't being found

reading sources... [100%] niscope/class
Didn't find abort in niscope.session
Didn't find acquisition_status in niscope.session
Didn't find add_waveform_processing in niscope.session
...

This can be fixed by specifying the class to which the method belongs.
Example:

.. py:method:: abort() becomes .. py:method:: Session.abort()

3. Attributes aren't being found

Didn't find absolute_sample_clock_offset in niscope.session
Didn't find acquisition_start_time in niscope.session
Didn't find acquisition_type in niscope.session
...

I could not determine how to fix this.

Steps to reproduce issue

1. In tox.ini, change docs: sphinx-build -b html -d {envtmpdir}/doctrees . ../generated/docs/html {posargs} to docs: sphinx-build -v -b html -d {envtmpdir}/doctrees . ../generated/docs/html {posargs}
2. Run tox -e clean
3. Run tox -e codegen
4. Run tox -e docs

You will see the issues mentioned above.