msrp.py: add a doc about reports

darcs-hash:20090218071734-b2873-e301e208197bc5bb87bfd4cc03370990a72827d8
MSRPChat: remove _initialize, add 'to' parameter __init__ and allow 'to' in send_message be None

darcs-hash:20090218104533-b2873-0a4646e7d7403c8c9c4c168c03eacb169c36135f