hyper v0.6

A bunch of goodies are included in version 0.6 of hyper.

Highlights

Experimental HTTP2 support for the Client! Thanks to tireless work of @mlalic.
Redesigned Ssl support. The Server and Client can accept any implementation of the Ssl trait. By default, hyper comes with an implementation for OpenSSL, but this can now be disabled via the ssl cargo feature.
A thread safe Client. As in, Client is Sync. You can share a Client over multiple threads, and make several requests simultaneously.
Just about 90% test coverage. @winding-lines has been bumping the number ever higher.

Also, as a reminder, hyper has been following semver more closely, and so, breaking changes mean bumping the minor version (until 1.0). So, to reduce unplanned breakage, you should probably depend on a specific minor version, such as 0.6, and not *.