Remove redundant "extern crate std"

This causes a compiler error on recent Rust versions.
Configure Git to ignore Cargo.lock

The lock file should not be checked into the repository for libraries.
Otherwise the locked versions therein could complicate the build for any
applications using the library.
Fix Cargo warning
Merge pull request #53 from hannobraun/master

Fix compiler error + smaller fixes
Minor fixes to Cargo build.
Merge pull request #54 from metajack/cargo-fixes

Minor fixes to Cargo build.
Update to the last rust-nightly.

Version of rustc: 0.12.0-pre-nightly (2e92c67dc 2014-08-28 23:56:20 +0000).