enconding: Add preferred option

[bjohansebas]

Use of the preferred option in encoding

There must be a backport to version 1, as it is a feature needed for expressjs/compression#194

[blakeembrey]

Honestly, I'm not super comfortable with this code as-is and would like to remove the variadic hack from the library instead of going deeper into it with options too.

[bjohansebas]

It was the way I found to avoid breaking compatibility and to be backward compatible. It took me a while to understand why it used arguments (it's the first time I see it), maybe it can be done in cleaner ways

[blakeembrey]

Ideally we get rid of that altogether, it's hard to understand, hard to fix, and worse for performance. I'd like to do it in a new major version. For now, I'm going to suggest you skip accepts altogether by doing: expressjs/compression#194 (comment). I think it's a better change anyway, and I won't need to maintain multiple releases of accepts this way.

[wesleytodd]

I will push to oppose a new major at this stage. This package is passed through to express and we cannot do more majors in these without incurring an unnecessary maintenance burden until we are preparing for a v6 release.

I agree with the proposed breaking change from @blakeembrey, just not the timing.