Docs improvements

[aamijar]

Continued overhaul of cuvs docs:

1. Separate Multi-GPU Nearest Neighbors docs into top level section with subpages.
2. Add docs for Multi-GPU All-Neighbors
3. Add Spectral Clustering and Spectral Embedding Python API docs (refer to cuml)
4. Add NN-Descent to C API docs
5. Change Bruteforce title to Brute Force KNN
6. Fix overload grouping on right sidebar
7. Fix doc treedepth
8. Separate Quantizer docs into subpages for each type
9. Various spelling, capitalization, and alphabetical ordering fixes.
10. Remove non-ascii characters (such as smart apostrophe)
11. Fix broken links

How to build docs locally

cd /home/coder/cuvs/cpp/doxygen && doxygen Doxyfile
cd /home/coder/cuvs/docs && make html
cd /home/coder/cuvs/docs/build/html && python -m http.server 8080

[cjnolet]

Oh I see- you put these out in the top-level for the C++ itself. Hmm. That's not awful. I think it's easier for users to find it this way. I think this is okay. When you said top-leve, I thought you measnt the top level index of the docs themselves.

I still wonder though- would this be better placed inside of the neighbors index? It seems like it'd make more sense there, rather than having it parallel to the other namespaces.

[aamijar]

Yeah, I was thinking it would be easier to find for users to have it moved up. But we can keep it in neighbors if you prefer.

[cjnolet]

I think I'd prefer if this was nested inside "neighbors".

[cjnolet]

Can you briefly describe what this change does?

[aamijar]

This is to fix point 6. Fix overload grouping on right sidebar.
For example instead of showing build a bunch of times, it shows build once. This used to work before without the change, but maybe there was some dependency update that made it stop working.
Ref: #1377