Doc improvements

[aamijar]

Introduces the following doc improvements:

1. Fix kmeans helpers not showing up correctly
2. Ensure pages are alphabetical under the different categories such as nearest-neighbors
3. Consistent subtitle naming from params to parameters
4. Fix python API multi gpu docs
5. New blogs and paper references
6. Fix missing struct members for preprocessing quantize
7. Fix typos and missing # from include

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[jameslamb]

Looks good!

FYI there's a linter called rstcheck that can catch some of the things you fixed (like subtitle formatting) in a pre-commit hook. We have approval to use it in RAPIDS and I've been wanting to try rolling it out at some point: rapidsai/build-planning#262

Want to try that here? (fine if it's a separate PR)

[aamijar]

Thanks James, sure, I can try that in another PR!

[aamijar]

/ok to test d62bb81

[tfeher]

LGTM, thanks aamijar!

[aamijar]

/merge