Update serialize

[Hoverbear]

rustc-serialize hit 3.0.

[BurntSushi]

No. rustc-serialize 0.3.x marks the start of using std::io. It is still recommended to use std::old_io. That recommendation alone wouldn't stop me, but there is still no support for standard IO in std::io, so I can't transition everything over yet.

I think once initial support gets into the next nightly, I'll be OK migrating.

[Hoverbear]

Okay, sounds good. I'm successfully using 0.3.x in my projects right now on this branch if anyone else can't use docopt with their projects.

To anyone else:
If you see something like Args does not implement Decodable when trying to use Docopt feel free to switch to it.

[BurntSushi]

Ah sorry, I forgot to update this issue. Standard IO is now in std::io, so Docopt is on rustc-serialize 0.3.0 now: #110

Note that you might still get this error if the reverse happens (you're pinned to 0.2.0).

[Hoverbear]

Sweet!