[reSIProcate] overview of recent changes to the stack

[Daniel Pocock <daniel@xxxxxxxxxxxxx>]

I've made some commits recently for Python, RADIUS and changes to the
authentication code

Just a couple of points to keep in mind:

- some of it is just cut and paste of existing code - large portions of
ReproAuthenticatorFactory.cxx were copied directly out of
ReproRunner.cxx - the main reason for this is so that people can
subclass AuthenticatorFactory in a plugin and also to improve
readability.  The authentication logic should perform exactly the same
way that it did before, it is just configured from a different class /
different source file.

- many things are optional.  Python and RADIUS support do not need to be
enabled - so anybody reviewing this code can completely ignore those
class files and just focus on the changes to the core classes (which are
in separate commits) and then look at the Python and RADIUS stuff in a
second pass.