Migrate from rustc-serialize to serde 1.0

[ordian]

This is a breaking change.

• decode() is renamed to deserialize()
  for consistency with serde
• docopt_macros is updated to latest nightly

Fixes #128, #213

[ordian]

Tests on Travis are failing on rust 1.12.
Any plans to drop support for this old version?

[BurntSushi]

This is awesome, thanks! This all looks pretty good. There are a couple nits that need to be resolved before bringing this in though.

Could you also please rebase and squash this PR down to a single commit when you're ready? Thanks!

[BurntSushi]

I understand why we can no longer use Rust 1.12 (serde_derive requires Rust 1.15 IIRC), but there's a reason why a specific version is tested in Travis: to ensure we don't accidentally bump the minimum Rust version required to build docopt. For this reason, please put the minimum version back. I think Rust 1.15 would be suitable.

[BurntSushi]

Please don't bump the version. I'll do that in a separate commit. :-)

[BurntSushi]

Same as docopt's Cargo.toml. I'll bump this version in a separate commit.

[ordian]

Fixed.
Bumped minimum rust version to 1.15, although I don't know why anyone would use stable, but not latest.
Also, replaced try! with ? (IIRC stable since 1.13).
Thanks!

[BurntSushi]

Thanks!

although I don't know why anyone would use stable, but not latest.

Because not everyone can upgrade everything all the time. Think about Linux distros, company policies, etc etc.

[ordian]

Should I revert version bump in readme as well?

[BurntSushi]

@ordian Yes please, good catch.

[ordian]

How about enum with struct variant support? E.g.

#[derive(Debug, Deserialize)]
enum CargoCommand {
    Build {
        flag_debug: bool,
        flag_examples: bool,  
    },
    Run {
        ...
    },
    Test,
    Bench,
    ...
}

[BurntSushi]

@ordian I'd prefer that be separate. It has been discussed quite a bit on the issue tracker, but all the details have fallen out of my head.

[BurntSushi]

Thanks! This is awesome work. :-)

[nixpulvis]

:DDDD