Shim protos and client for containerd

TTRPC bindings for containerd's shim events and interfaces.

Look and feel

Basic client code looks as follows:

```rust let client = client::Client::connect(socketpath)?; let taskclient = client::TaskClient::new(client);

let context = client::ttrpc::context::with_timeout(0);

let req = client::api::ConnectRequest { id: pid, ..Default::default() };

let resp = task_client.connect(context, &req)?; ```

Example

Have a look on example here.

bash $ cargo build --example connect $ sudo ./connect unix:///containerd-shim/shim_socket_path.sock