_siftup and _siftdown implementation

[Sven R. Kunze]

Hi srinivas,

I wrote this simple benchmark to measure comparisons:

import random

from xheapimport RemovalHeap


class X(object):
     c =0 def __init__(self, x):
         self.x = x
     def __lt__(self, other):
         X.c +=1 return self.x < other.x

n =100000 for jjin range(5):
     items = [X(i)for iin range(n)]
     random.shuffle(items)
     heap = RemovalHeap(items)

     random.shuffle(items)
     for i  in items:
         heap.remove(i)

     print(X.c)
     X.c =0


old version:
430457
430810
430657
429971
430583

your pull request version:
426414
426045
425437
425528
425522


Can we do better here?

Best,
Sven