Multi-processing

I've done a quick proof of concept on a local copy of the code (not going to be changed on the svn repository, until I make a decision). It is relatively trivial to set up plugins to run in separate threads. Though perl's pretty brain dead method of threading makes this quite hard and kludgy. (You have to share non-complex variables to pass data 'twixt the parent and the thread. If you want anything more complicated than a hash then you're out of luck).

This also makes it trivial to add key presses to return status indicators, alter verbosity etc.

This leaves some questions that need answers to: * Number of threads needed * Way of passing %age complete for each plugin * Do we want sub-threading of plugins (e.g. nikto_tests.plugin takes so much longer than any other plugin) * mark counters don't work due to aforementioned perl brain deadness in use of complex variables