Rewrite header recipes for hyper 0.12

[AndyGauge]

Apparently, changes have been made to hyper 0.12 that breaks the header! implementation. Those changes should be reviewed and implemented into the recipes. Documentation is being moved to doc.servo.org until the recipes have been revamped.

Check out the changelog

[budziq]

Currently two examples using custom headers are broken:

• trivial single custom headder
• three typed headders for github rate limmiting

As there are several ways to approach the implementation I'd like to pick @seanmonstar 's brain for suggestion on what would be the most idiomatic approach for custom header definition for our readers to learn from.

cc https://github.com/seanmonstar/reqwest/issues/312

[seanmonstar]

Typed headers are being working on as a new crate: https://github.com/hyperium/headers

In the mean time, I might suggest removing the recipes completely. I'd expect the new crate to show how to create a new header type in its documentation.

[budziq]

Thanks a lot for the info @seanmonstar! I guess that we will hide the examples (https://github.com/rust-lang-nursery/rust-cookbook/pull/430) and revert them once the custom header story is sorted out on hyper side. What are your thoughts @AndyGauge ?

[AndyGauge]

Sounds like a plan of action. We can leave this open as a reminder once headers lands.