rpm v0.8.14 breaks advertised minimum compatible rust version

[michaelb]

Hi!

It looks like between 0.8.12 and 0.8.14 a change was introduced that broke compatibility with older Rust version.

Latest stable (1.71) works fine, but 1.65 (my own project's MSRV) not so much, let alone rust 1.56 as this repo's README mentions.

There does not appear to be a consensus on how to deal with increasing one's library MSRV, and I don't necessarily expect you to match it with a 'breaking' change in versionning (semver-wise).

Could you document the correct minimum supported rust version you support currently (and ideally intend to keep supporting) ?