Add getters for current configuration values

[shahn]

This was inspired by suggestions provided in #598, thanks a lot to @VictorKoenders.

Fixes #598.

[codecov[bot]]

Codecov Report

Attention: 29 lines in your changes are missing coverage. Please review.

Comparison is base (dd82a9c) 57.32% compared to head (9763ccd) 57.24%.

Files	Patch %	Lines
src/varint/decode_unsigned.rs	68.91%	23 Missing :warning:
src/config.rs	0.00%	6 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## trunk #681 +/- ## ========================================== - Coverage 57.32% 57.24% -0.08% ========================================== Files 51 51 Lines 4344 4350 +6 ========================================== Hits 2490 2490 - Misses 1854 1860 +6 ```

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[VictorKoenders]

Sorry for the late response, I was going to think about this over the weekend and then Factorio happened and now it's a month later.

A couple of things we've been thinking about:

• Not sure what derive attributes we want on the enums, PartialEq, Eq is maybe not needed, Clone or Debug might be? We're not sure
• It would be nice if we could have const fn in traits. We were thinking of adding #[inline(always)] to the implementation functions but I don't want to do that before we actually benchmark that it is faster/slower, and I think that's outside of the scope of this PR.

Other than that it looks good, thanks for the contribution!

[shahn]

Thanks for the merge, I think PartialEq and Eq are needed to ensure you can actually do something with the config values. Debug could be nice, but is not required to do something useful. Or perhaps I misunderstood your question?

[VictorKoenders]

You understood my question correctly.

I think PartialEq and Eq are needed to ensure you can actually do something with the config values

You can still match on the variants. This is what we do in bincode currently, the following code will still work without PartialEq, Eq:

                Ok(match D::C::ENDIAN {
                    Endianness::Little => u16::from_le_bytes(bytes),
                    Endianness::Big => u16::from_be_bytes(bytes),
                })

But this will not:

if D::C::ENDIAN ==  Endianness::Little {
    panic!("Only big endian supported");
}

But I'm also not sure if there's a downside to adding this