Help, naming and repl changes

Changed to using independent __help__ attribute rather than docstrings;
added Help class to hold unaffiliated help.
Changed all functions to use lower_with_underscores naming, so that
they're more consistent with the CLI commands.
Added support for multi-line commands, which was needed to allow
definition of functions (and classes).
Added load command.

To use the Python command line effectively, you need to be able to load
code.  This function does that.
Change to use class for constants

The class provides online help support, in addition to matching with
strings as was done previously.
Begin creation of event hierachy

Add event sub-classes for close, recv and accept.
Comment the packet dump function
Better error display; better parameter checking for breakpoints.