Legacy Pruning and Send API Improvements

The following items were addressed in this large update:

- Remaining legacy handshake code was removed.
- A bug in sending an initial message was fixed, where if send() was called multiple times immediately, only the last message would be delivered.
- Extended the send() API to allow a single JSON object to be used as the only argument, mapping method names to data. This is useful if one send() invocation should hit multiple endpoints.
- Fixed a few demo config values.
- Updated the README.