Option to skip roxygen skeleton generation

[noamross]

I and my team rarely use the roxygen skeleton created with functions when we create them for targets workflows rather than packages, and if we do usually do so after the function is written and often the arguments no longer apply. How about an option (set by an option or env var) to skip the roxygen block?

Happy to PR this myself.

[MilesMcBain]

Sounds good happy to accept a PR 👍