Consider using downloads in the last N days, instead of all time.

TL;DR: We use the top 100 crates based on all time downloads to avoid being arbiters of what crates are available. If you think that a "popular" crate should be present on the playground, consider enhancing crates.io to have an API that would prioritize crates downloaded in a more recent interval.

Rationale

See discussion started in #82 —

I'm hesitant to start cherry-picking crates for inclusion based on my own whims. If I were to do that, I'd certainly blacklist xml-rs in favor of my own XML parser 😈

Additionally, I think about how I'd explain to someone why a given crate is available or not. If it's "someone submitted a PR", then I fear we'd be compiling 1000s of crates every night. If it's "the maintainer picked it", then I fear the backlash directed towards me on public (and private?) forums.

And #113 —

We've also toyed around with the idea of having "sponsored crates", where someone contributes money towards server costs (which are paid out of our own pocket at the moment), but strangely no one seems excited to pay for it ;-) If you are, I'm sure we can get in contact.

No repository file, test, or entry point is identified. Start by reviewing the linked discussions in #82 and #113, then determine whether the proposed recent-downloads API belongs in this repository; done would require an agreed, actionable scope.