Updates a chat item to the chat section of the site. If no datestamp is given the original is not reset
Location: http://hackdaylondon07.backnetwork.com/api/1.0/updateChat.aspx
apikeystringrequired
chatidintrequired
personidintrequired
messagestringrequired
datestampISO date
externalsourcestring
externalusernamestring
externalidint