Update message sending documentation.

[barberdt]

In the documentation for the participation API, we need to update it so that developers are aware that, when sending a message, the message chunk must have an extra '\r\n' at the end of it. That is, when the final message is sent, it should have two '\r\n's at the end of it. However, the size of the message should be calculated for the message with only one of those carriage returns.

[c4milo]

If anybody wants to know why we had to come up with our own framing, feel free to read http://tools.ietf.org/html/rfc6202.

Specifically:

3.2. HTTP Streaming Issues

Framing Techniques: Using HTTP streaming, several application
messages can be sent within a single HTTP response. The
separation of the response stream into application messages needs
to be performed at the application level and not at the HTTP
level. In particular, it is not possible to use the HTTP chunks
as application message delimiters, since intermediate proxies
might "re-chunk" the message stream (for example, by combining
different chunks into a longer one). This issue does not affect
the HTTP long polling technique, which provides a canonical
framing technique: each application message can be sent in a
different HTTP response.