Ready for 3.6.0 PyPI/GitHub release

[alisnwu]

PyPI/GitHub rc-release preparation checklist:

• All PRs/issues attached to the release are merged.
• All the badges on the README are passing.
• License information is verified as correct. If you are unsure, please comment below.
• Locally rendered documentation contains all appropriate pages, including API references (check no modules are
  missing), tutorials, and other human written text is up-to-date with any changes in the code.
• Installation instructions in the README, documentation and on the website (e.g., diffpy.org) are updated.
• Successfully run any tutorial examples or do functional testing with the latest Python version.
• Grammar and writing quality are checked (no typos).

Please mention @sbillinge here when you are ready for PyPI/GitHub release. Include any additional comments necessary, such as version information and details about the pre-release here:

PyPI/GitHub full-release preparation checklist:

• Create a new conda environment and install the rc from pypi (pip install <package-name>=??)
• License information at Pypi is verified as correct.
• Docs deployed successfully to <package-name>.github.io
• Successfully run all tests, tutorial examples or do functional testing

Please let @sbillinge know that all checks are done and package is ready for full release.

conda-forge release preparation checklist:

• Ensure that the full release has appeared on Pypi successfully
• New package dependencies listed in conda.txt and test.txt are added to meta.yaml in the feedstock.
• Close any open issues on the feedstock. Reach out to @bobleesj if you have questions
• let @sbillinge and @bobleesj when this is ready

Post-release checklist

• Run tutorial examples and conduct functional testing using the installation guide in the README. Attach screenshots/results as comments.
• Documentation (README, tutorials, API references, and websites) is deployed without broken links or missing figures.

[bobleesj]

@alisnwu Since we are planning for 3 6.0, for now, we could close this issue and re-open or create a new one later when we are ready?

[sbillinge]

I just edited the title.