First implementation

It is somewhat working, theorically Hunk_Begin returns a new chunk of
memory and Hunk_Alloc returns an offset pointer to it (relative to the
chunk size requested) and Hunk_Free does the actual release of memory.
It is working on mi Linux box although it needs serious revisionas it is
maybe unpredictable.
hunk_driver

New cvar "hunk_driver" returns the name of the actual Hunk allocator
being currently use.