Add consume() recipe to itertools docs.

Doc/library/itertools.rst

@@ -635,6 +635,10 @@ which incur interpreter overhead.
        "Return function(0), function(1), ..."
        return imap(function, count(start))
 
+   def consume(iterator, n):
+       "Advance the iterator n-steps ahead. If n is none, consume entirely."
+       collections.deque(islice(iterator, n), maxlen=0)
+
    def nth(iterable, n, default=None):
        "Returns the nth item or a default value"
        return next(islice(iterable, n, None), default)