Create tokio-codec (#360)

Create a new tokio-codec crate with many of the contents of
`tokio_io::codec`.

tokio-codec/README.md

@@ -0,0 +1,35 @@
+# tokio-codec
+
+Utilities for encoding and decoding frames.
+
+[Documentation](https://docs.rs/tokio-codec)
+
+## Usage
+
+First, add this to your `Cargo.toml`:
+
+```toml
+[dependencies]
+tokio-codec = "0.1"
+```
+
+Next, add this to your crate:
+
+```rust
+extern crate tokio_codec;
+```
+
+You can find extensive documentation and examples about how to use this crate
+online at [https://tokio.rs](https://tokio.rs). The [API
+documentation](https://docs.rs/tokio-codec) is also a great place to get started
+for the nitty-gritty.
+
+## License
+
+This project is licensed under the [MIT license](LICENSE).
+
+### Contribution
+
+Unless you explicitly state otherwise, any contribution intentionally submitted
+for inclusion in Tokio by you, shall be licensed as MIT, without any additional
+terms or conditions.