Use core::result instead of std::result in order to make it work in a…

[daym]

… no_std environment.

This pull request would avoid using std::result, instead favoring core::result, in order to make FromStr work in a no_std environment.

[Peternator7]

LGTM 👍 Thanks for the improvement

[Peternator7]

Released in version 0.23! Thanks for the PR. https://crates.io/crates/strum

[daym]

Thank you for the release.

Unfortunately, it does not work since there are now more references to std::convert and so on in the generated code (i.e. inside quote!)--in the same file at the bottom (the ones in try_from_str were added only after my change).

I recommend adding a simple integration test for the no_std environment.

error[E0433]: failed to resolve: could not find `std` in the list of imported crates
   --> src/ondisk.rs:147:56
    |
147 | #[derive(Debug, PartialEq, FromPrimitive, Clone, Copy, EnumString)]
    |                                                        ^^^^^^^^^^ could not find `std` in the list of imported crates
    |
    = note: this error originates in the derive macro `EnumString` (in Nightly builds, run with -Z macro-backtrace for more info)

[Peternator7]

Sorry about that, merged the other PR. Will add integration test when there's time.