Update to new rust syntax.

`pub extern' is now obsolete. The `pub' modifier must be specified for each individual items.
as_c_str is now a method.
Merge pull request #12 from sebcrozet/master

Update to new rust syntax.
Style fix
More Rust version updates
Merge pull request #13 from kmcallister/rust-upgrade

More Rust version updates
Switch from -o to --out-dir.
Revert to using -o for tests
Merge pull request #14 from kmcallister/otest

Revert to using -o for tests