Update to Serde 1.0

[dtolnay]

Release notes for 0.9.0: https://github.com/serde-rs/serde/releases/tag/v0.9.0
Release notes for 1.0.0: https://github.com/serde-rs/serde/releases/tag/v1.0.0

[cuviper]

I think this is likely a breaking change, but if there's any way to conditionalize our code to cover a wide range of serde versions, maybe we can squeeze by.

[dtolnay]

Technically it's definitely possible but I'm not going to recommend that you do it. 🤣

The way to do it would be make a serde-0-9 crate and a serde-1-0 crate that each depend on the respective version of serde and just contain extern crate serde; pub use serde::*. Then you could provide an impl for serde_0_9::Serialize as well as serde_1_0::Serialize.

[cuviper]

Oy. I was thinking more along the lines of detecting the selected serde version in a build script somehow, and just emit a feature name for that. But maybe that's not possible.

We need to do a semver bump. I've been procrastinating that forever. Maybe stable i128 will finally be worth advancing num so we don't have that major lack.

[cuviper]

We could do it as a separate num-serde crate, like url does with url_serde.

[corngood]

So I've got local changes for serde 1.0, and I was hoping to make a PR.

It seems like the options are:

1. bump to 0.2 and require serde 1
2. support both with features (trying to wrap my head around that one)
3. support both with intermediate crates
4. wrapper crate (num_serde)

The changes are pretty trivial if we do (1), but I don't see a PR/branch with them. Would you like me to push it so it can be linked to the 0.2 milestone? If not, would you like me to take a look at one of the other options?

[cuviper]

We need to just do 0.2. I hate to force an upgrade on the ecosystem, but it's going to happen sometime. We'll do it in a side branch so we can batch as many breaking changes as we can at once.

To that end, there's now a next branch, and #302 to get it going. When that lands, you can send a PR for next instead of master with the breaking change. Serde 1 only, still behind an optional feature, and probably remove rustc-serialize while we're at it. Sound good?

[cuviper]

This is done on the next branch.