Support multi-workspace repositories

[newpavlov]

In RustCrypto we have repositories with mixed editions (e.g. see the traits repo). To allow testing of MSRV we have temporarily moved 2021 edition crates into their own workspaces (e.g. see the kem crate). Unfortunately, deps.rs analyzes only the root workspace, so such crates are getting skipped as can be seen on the relevant page: https://deps.rs/repo/github/RustCrypto/traits

[Feliix42]

I know that this has been open for a while but I think it's a quite interesting problem. I was asking myself if there could be situations in which you would not want to recursively traverse the repository for other Cargo.toml files.

From the top of my head I cannot remember if we're actually pulling the whole repo or just the Cargo.toml, though. The latter would complicate matters a bit when it comes to recursive traversals.