move percent_encoding to its own crate

[seanmonstar]

• I arbitrarily chose percent_encode, but I could update it to be percent_encoding if preferred.
• The macro define_encode_set duplicated, to maintain backwards compatibility for url.
• I set it 1.0.0 since this is a public dependency of url, and so it can't make API breaking changes easily without affecting url.

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This change is 

[nox]

Good stuff, few comments.

[nox]

Why does this need to be done here?

[seanmonstar]

Um, I have no idea why this is here...

[nox]

Isn't there a way to reexport a macro from a different crate?

[SimonSapin]

IIRC the only way on current stable Rust is pub use some_crate::*;, which of course also re-exports other things.

[seanmonstar]

There's #[macro_reexport], which is unstable, and there's a the glob trick, which I'm still not certain is on purpose, but still, it re-exports too many things, so duplicating the macro seems required...

[seanmonstar]

@nox you said in IRC you prefer the glob trick. To reiterate, that requires a pub use percent_encoding::* inside the url root. That would suddenly make all the things normally in that module/crate pollute the url namespace. Suddenly there is url::SIMPLE_ENCODE_SET, besides url::percent_encoding::SIMPLE_ENCODE_SET and friends.

[nox]

Can't you just put the macro in a submodule of percent_encoding and glob import that module from both percent_encoding and url?

[seanmonstar]

That's possible, but puts another public (useless) module in the percent_encoding crate. Of all the possible options, I find just redefining the macro in url to be the best.

[nox]

Given both crates are in the same repository, IMO it is better to just make a #[doc(hidden)] module and avoid the duplication of the macro, but I'll let @SimonSapin the final say.

[seanmonstar]

When macros 2.0 arrive (already major pieces in nightly!), they can be named explicit, so it could eventually just become in url pub use percent_encoding::define_encode_set;.

[nox]

Unfortunately I don't think these two crates can really afford to rely on hot new stuff, given how central it is to the ecosystem.

[seanmonstar]

We can cross that bridge when we get there, but this crate has already made upgrades to 1.15, and other than using the newest the day after, it seems to be fine to upgrade to newer version.

[nox]

I'll let @SimonSapin decide on the crate name.

[nox]

11:10 <•SimonSapin> nox: if we’re splitting hairs, I think "encoding" is the general mechanism and the two specific (opposite) operations are "encode" and "decode"

Let's name it percent_encoding.

[SimonSapin]

I arbitrarily chose percent_encode, but I could update it to be percent_encoding if preferred.

I’m kind of splitting hairs, but I’d prefer percent_encoding. I think "encoding" refers to the general mechanism, which includes two opposite operations: "encode" and "decode".

[seanmonstar]

Renamed to percent_encoding, stray code in url_serde removed.

[seanmonstar]

@SimonSapin or @nox, r?

[bors-servo]

☔ The latest upstream changes (presumably #335) made this pull request unmergeable. Please resolve the merge conflicts.

[SimonSapin]

Landed in #362. Thanks!