Update for rust-0.13-nightly and latest rust-sdl2.

    * Rename fail! to panic!
    * Remove occurrences of "use std::owned::Box".
    * Renderer<T> is now just Renderer in rust-sdl2.
    * Rename lint from "ctypes" to "improper_ctypes".
Merge pull request #12 from bfabio/rust-0.13-nightly

Update for rust-0.13-nightly and latest rust-sdl2.