Python bindings for KeyPoint methods

Usage:

import numpy as np
import cv2
img = cv2.imread('messi5.jpg',0)
sift = cv2.SIFT()
kp = sift.detect(img)

pts = cv2.KeyPoint_convert(kp)

kps = cv2.KeyPoint_convert(pts.reshape(-1,1,2))

overlap = cv2.KeyPoint_overlap(kp[0],kp[1])
warning corrections
alignment of parameters as per speclad
Merge pull request #1373 from abidrahmank:pykeypoints
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  alignment of parameters as per speclad
  warning corrections
  Python bindings for KeyPoint methods