Rust 1.0 and nanomsg.rs master branch

[blabaere]

Since some public parts (Reader, Writer, Duration ...) of nanomsg.rs won't make it in Rust 1.0, we will probably end up with a branch for the Rust 1.0 and another one for Rust nightly.
@thehydroimpulse Which one should be the master ?

[thehydroimpulse]

@blabaere Sorry for the delay, just got back from holidays. Master should probably track Rust nightly and we can have a 1.0 branch to track 1.0

[blabaere]

PR#88 introduces the stable_1.0 branch and to celebrate this, it gets rid of link-config (and its weekly build break)