Release v0.6.0 and v0.6.1

[nkeim]

Thanks for everyone's patience and for your contributions to this release! I tagged the release candidate v0.6.0rc1. I plan to do the stable release late next week (e.g. Feb. 23). In the meantime, as you are able, please check out

• The PyPI page, which includes a distribution that will be used for the pip and conda packages.
• The built documentation, including the release notes

Next steps (mostly following the release checklist.

• [x] Tag the final release, build, and publish on PyPI
• [x] Verify that the conda packages built correctly
• [x] Merge the corresponding trackpy-examples PR
• [x] Rebuild and upload the documentation and make these the stable docs

[nkeim]

A breaking change in Zenodo since the last release made it necessary to re-release this version as v0.6.1 in order to have a DOI. Conda packages for v0.6.0 were never published.

The only changes were to the Zenodo metadata and the release notes, in #723 and #724.

[nkeim]

The PyPI and conda packages are now available, and I've confirmed they are sufficient for import trackpy. Thanks again for your contributions and for your patience, everyone!