Update to latest Rust
Derive Copy wherever sensible

Copy is now opt-in, see [1]. To keep the current library functionality it is
derived for all sensibly copyable types.

[1]: https://github.com/rust-lang/rust/commit/096a28607fb80c91e6e2ca64d9ef44c4e550e96c
Merge pull request #53 from aepsil0n/update_nightlies

Update to latest Rust
Update to the last rust-nightly.

Version of rustc: 0.13.0-nightly (42deaa5e4 2014-12-16 17:51:23 +0000).

Fix #54.
Merge pull request #55 from sebcrozet/rustup

Update to the last rust-nightly.