Upgrade to roxygen2 7.3.0

[jdblischak]

Closes #313

It turns out that if I remove the quotes around := and %>%, then the NAMESPACE is correctly generated by both roxygen2 7.2.3 and 7.3.0

[nanxstats]

Although I'm often reluctant to suggest changes that would lead to large-scale changes (such as requiring 10+ PRs to update all packages), looks like we may need a path forward here before the next roxygen2 release, and this might be the only way.

I hope roxygen2 > 7.3.0 will fix the bug to support with quotes and keep supporting without quotes so we don't need to change this back. 🤞

[jdblischak]

requiring 10+ PRs to update all packages

I view this as a temporary problem. Thus we only need to update packages that are being actively developed

I hope roxygen2 > 7.3.0 will fix the bug to support with quotes and keep supporting without quotes so we don't need to change this back.

That's why I tested with roxygen2 7.2.3. The unquoted version worked before, currently works, and will continue to work. And I'm less worried about future problems since the PR r-lib/roxygen2#1574 is adding tests for all the various use cases (no quotes, single quotes, double quotes, and back ticks)