Add a broadcast API.

Alerts the web socket handler to the need to broadcast a message to
some or all of the connected web sockets.  It is up to the developer
to keep track of the connected sockets.
Merge pull request #231 from davidw/websocket_broadcast

Add a broadcast API.
Prep for 0.8.5
Just use latest ErlyDTL
Document "compiler_options"
Fix bug in JSON generation
Update testing docs