MSRV policy

[daxpedda]

Considering #581 and #671 it might be useful to introduce an official MSRV policy.

[gwenn]

I would prefer not to have a MSRV.
Allow any incompatibility in major releases.
But, make sure that minor releases don't break X ? X = stable Rust version used by previous release ?
Because it is easier to follow only stable Rust releases.
See rusqlite/rusqlite#566

[daxpedda]

That's a common MSRV policy.
E.g. https://github.com/RustCrypto/traits/tree/master/elliptic-curve#minimum-supported-rust-version.

Sounds good to me.

[gwenn]

Even minor releases can change MSRV ?
But still, you need to check patch releases...

[daxpedda]

I'm a bit confused, do you want to keep the MSRV between patch releases or minor releases?

But yeah, you are not gonna be able to enforce it without setting up checks in CI probably.

In any case, any MSRV policy is better then none, even if you don't want to follow any MSRV at all.