Document which exceptions are thrown during send/receive

[bitc]

The haddocks for receiveDataMessage say that this function can throw ConnectionException under various conditions.

But it is not clear if there are any other exceptions that can occur. The following issues seem to hint that it is also possible for lower level socket exceptions or SSL exceptions to bubble up: #69 #75 . We need proper documentation that tells us a complete list of which exceptions we can expect. (It is not totally clear to me from looking through the source code)

Same goes for the send* family of functions.

Thank you

[jberryman]

I don't agree we need a "complete list of exceptions" that might be thrown (we have an exception system in the first place because this isn't really an attainable goal...), but would like some clarity on whether we should expect socket errors