Update to the last Rust: remove the float type.

This replaces float by f32 when glfw needs a c_float.
This replaces float by f64 when glfw needs a c_double.
Merge pull request #36 from sebcrozet/remove_float

Update to the last Rust: remove the float type.
Switch to using f64 in examples
Merge branch 'master' of git://github.com/bjz/glfw-rs into q3