Rewrite ipsilon.util.policy.Policy class documentation
    
    Rewrite docstring documentation of the Policy class to be easier to
    understand, more accurate, with examples.  Also fleshes out inline
    comments to make the code a bit easier to follow.
    
    Fixes ticket #178
    Merges: #113
    Signed-off-by: Howard Johnson <merlin@merlinthp.org>
    Reviewed-by: Patrick Uiterwijk <puiterwijk@redhat.com>