[DOC]Add missing functions to API docs Index

[samukweku]

PR Description

Please describe the changes proposed in the pull request:

• Add drop_constant_columns and factorize_columns to the API

This PR resolves #871 .

PR Checklist

Please ensure that you have done the following:

1. PR in from a fork off your branch. Do not PR from <your_username>:dev, but rather from <your_username>:<feature-branch_name>.

2. If you're not on the contributors list, add yourself to AUTHORS.rst.

3. Add a line to CHANGELOG.md under the latest version header (i.e. the one that is "on deck") describing the contribution.
   • Do use some discretion here; if there are multiple PRs that are related, keep them in a single line.

Automatic checks

There will be automatic checks run on the PR. These include:

• Building a preview of the docs on Netlify
• Automatically linting the code
• Making sure the code is documented
• Making sure that all tests are passed
• Making sure that code coverage doesn't go down.

Relevant Reviewers

Please tag maintainers to review.

• @ericmjl

[codecov]

Codecov Report

Merging #872 (62e26dc) into dev (5e2ccb3) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##              dev     #872   +/-   ##
=======================================
  Coverage   94.89%   94.89%           
=======================================
  Files          19       19           
  Lines        2078     2078           
=======================================
  Hits         1972     1972           
  Misses        106      106           

[ericmjl]

Only one small request, @samukweku - our config for pytest is in pyproject.toml!

Other than that, I think we're good to go 😄.

[ericmjl]

This being a docs PR, it's sufficient to have one review on it. I think we need to be a bit more conscientious with code reviews. Therefore, I merged with only myself as an official reviewer.

Thanks @samukweku! 🎉