Release v3.1.3: clarify error message (fixes #14)

Release v3.1.2

Don't send id in notifications (fixes #8)

Omitting a callback should omit the id from the outgoing request.  Also,
cleaned up unnecessary discardSerial concept.

Release v3.1.0

Create .notify(), remove useless timers (fixes #6)

Bump to v3.0.1-beta

Specify language