We have a lot of references in our docstrings and guides that

incorrectly pointed to the target. In some cases this is due to typos,

or using the full module path instead of the one provided in docs, or

old docs that didn't attempt to use the full name. There are also

__init__.py files that are importing and re-exporting classes and

functions, and these were getting picked up and causing issues.
This change fixes up most of these by turning on Sphinx's nitpick

setting and working my way through the reference issues. This does not

fix everything, partly due to issues in third-party docs and strangeness

with Sphinx, but it takes care of the big culprits we have control over.

Generated the docs with nitpick on. Saw that issues I fixed were gone,

and that the links for the ones I went through were resolving.