Arrange cannonical

[dajmcdon]

Checklist

Please:

• Make sure this PR is against "dev", not "main" (unless this is a release
  PR).
• Request a review from one of the current main reviewers:
  brookslogan, nmdefries.
• Makes sure to bump the version number in DESCRIPTION. Always increment
  the patch version number (the third number), unless you are making a
  release PR from dev to main, in which case increment the minor version
  number (the second number).

Change explanations for reviewer

• Makes new_epi_df() column order match key_colnames() ordering.
• Adds an internal function to locate columns in canonical order, and arrange rows in that order. Resolves epi_df structure #482
• Cleans up some Roxygen documentation that was producing warnings/notes in R CMD Check

[dajmcdon]

@dsweber2 Can you take a look at the snapshot errors in the check above? This PR shouldn't touch those, so I'm not sure what's right or wrong.

[dsweber2]

It's changing the default order of the columns, so the snapshot is getting put in a different order. The actual content of the tibble is the same, I checked. I just pushed a commit that records that.