Review Depth

[srittau]

I'd like to add short guidelines to the maintainer's section of CONTRIBUTING about how thorough a PR should be reviewed, but we need to agree on that first. My personal take (not final wording):

• Auto-generated stubs: just do a brief scan for red flags, ignore possible improvements to keep contribution bar low.
• Large hand-crafted PRs like my recent 3.8 PRs or the cryptography PR: while maintainer's are free to delve into it as deeply as they wish, mostly look for red flags, general issues, and do spot checks.
• Smaller hand-crafted PRs: Do a thorough review.