Provide `put_ne` and `get_ne` implementations for native endianness

[lehmanju]

Thank you for providing this crate. The API is really intuitive, however, for some projects there is a feature I am missing: support for native endianness.

Right now Buf and BufMut provide put and get functions for big and little endianness. But some protocols, like wayland, rely on native endianness. This makes parsing and serialization difficult with bytes.