Added tar_renv

[mattwarkentin]

Prework

• I understand and agree to the code of conduct and the contributing guidelines.
• I have already submitted an issue to the issue tracker to discuss my idea with the maintainer.

Summary

Add the tar_renv() function and documentation as discussed in #157. PR also includes unit tests and the addition of tar_renv to _pkdgown.yml.

Related GitHub issues and pull requests

• Ref: Handling large data sets in a pipeline #157

Checklist

• This pull request is not a draft.

[mattwarkentin]

── R CMD check results ───────────────────────────────── targets 0.0.0.9000 ────
Duration: 1m 39s

❯ checking for future file timestamps ... NOTE
  unable to verify current time

0 errors ✔ | 0 warnings ✔ | 1 note ✖

[mattwarkentin]

Still one more lint complaint at https://github.com/wlandau/targets/pull/170/files#diff-2952800a4992b3e5427b2bad378bfd3fR31

I think this one is unavoidable...

[wlandau]

This is off to a great start, thanks for contributing. I know I have a lot of comments, but they are all minor.

By the way, feel free to add yourself as a contributor in the DESCRIPTION file, e.g. person(given = "Matthew", family = "Warkentin", role = "ctb").

[wlandau]

Also, don't worry about the check note in #170 (comment). That one is truly unavoidable.

[mattwarkentin]

Thanks for all the comments! No sirens went off this time, so I must be learning how to do all my checks BEFORE committing the code.

[wlandau]

Looks great, thanks for your work.

[mattwarkentin]

Thanks for allowing me to go through this process. You probably spent more time reviewing my code than it would've taken you to implement this feature yourself, so I do appreciate it.