Make AVA, RDN & DN comparison case insensitive. No need for lowercase normalization.
    
    Replace deepcopy with constructor (i.e. type call)
    Can now "clone" with configuration changes by passing object
    of the same type to it's constructor, e.g.
    dn1 = DN(('cn', 'foo'))
    dn2 = DN(dn1)
    dn2 = DN(dn1, first_key_match=False)
    
    Remove pairwise grouping for RDN's. Had previously removed it
    for DN's, left it in for RDN's because it seemed to make sense
    because of the way RDN's work but consistency is a higher goal.
    
    Add keyword constructor parameters to pass configuration options.
    
    Make first_key_match a configuration keyword.
    
    Updated documentation.
    
    Updated unit test.
    
    FWIW, I noticed the unittest is now running 2x faster, not sure why,
    removal of deepcopy? Anyway, hard to argue with performance doubling.