New way to store messages

Using a dict of lists (time -> messages) and a sorted list (times)
instead of an unsortable list of tuples
Only export the chat listener interface

Avoids remote shell cores to try to access exported shell commands
Allow unquoted sentences in the shell command 'post'
Corrected a method call
Custom serialization for Message beans

Tells jsonrpclib the arguments required by the constructor
Moved Message bean definition to chat.constants
Updated readme