- Eliminate some calls to unwrap(), in favor of saner error handling.
- Eliminate dependency on capnp/c++.capnp.
- Directly include rpc.capnp and rpc-twoparty.capnp to make the build more robust.
- Fix "unimplemented" panic that could happen on certain broken capabilities.
- Fix bug where piplining on a method that returned a null capability could cause a panic.