Consider to use the lowest possible Rust version

[qarmin]

Most of libraries which I used, needed to use the lowest possible Rust version(usually support latest 10 versions, so if newest is 1.58, latest supported is 1.48)

Lofty currently require Rust 1.57.0, which is only 1 release behind official Rust release.

To pack software for Ubuntu 20.04 I need to use specific Rust version, 1 week ago it was Rust 1.53.0, but now it is Rust 1.57.0(https://packages.ubuntu.com/search?keywords=rust&searchon=names&suite=impish&section=all)

For future I think that it would be great if lofty would pin to some older version of Rust to help to package apps which use this libraries on older/specific OS.

[Serial-ATA]

Hm, I hadn't thought about setting a MSRV. While I don't want to speak too early, I don't think it'll need to go above 1.57 anytime soon, since I just needed it for try_reserve. I can't guarantee that till 1.0, though.

And I wasn't aware that some distros were that far behind, thanks for bringing that to my attention. I'll take that into consideration if I do ever try to bump the version.

[qarmin]

Looks that lofty needs now Rust 1.65.0 due rust-lang/rust#96709

error[E0658]: generic associated types are unstable
   --> /home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/lofty-0.10.0/src/traits.rs:137:2
    |
137 | /     type RefKey<'a>
138 | |     where
139 | |         Self: 'a;
    | |_________________^
    |
    = note: see issue #44265 <https://github.com/rust-lang/rust/issues/44265> for more information

[Serial-ATA]

It's unfortunate how far behind Ubuntu is, 1.65.0 is almost 2 months old at this point. Do they have a rule that they only push out the 4th release of rustc? Having gone 1.57.0 -> 1.61.0, I'd assume 1.65.0 is on its way sometime soon?

[Serial-ATA]

The Rust version is now explicitly set to 1.85 with #513