Update to unboxed closures
Update to native OS threads

Use std::thread rather than std::task. Also remove comments about paying special attention to natively blocking I/O (which was an issue with libgreen, but isn't anymore with native threads).
Update cargo manifest with more information
Use assert_eq! in argument tests
Fix indentation of reply test data
Don't compile examples as part of the package

Examples are not binaries of the package, so don't build them by default (they're still build automatically by `cargo test`)
Add test for as_bytes with tuple of structs
Compare paths in argument tests rather than their string representation