This is a minimal effort to get things running. Only the `beam` package
has changed - backend code is untouched.
- The `beam` package is still around, but functions as a
libswarm-specific wrapper around libchan messages. It'll either be
renamed or moved to the top-level namespace.
- We have our own Message type which serializes/deserializes to libchan
messages, and our own versions of Sender and Receiver which speak
libswarm. WrapSender and WrapReceiver promote libchan objects to
their libswarm equivalents.
- We also have our own wrappers around libchan utilities: RetPipe,
Handler, Pipe, Copy.
Signed-off-by: Aanand Prasad <aanand.prasad@gmail.com>