Make RANSAC Homography estimation faster

The code is minimal but it has a great impact in the speed of RANSAC homography estimation. And it could be important in CPU limited platforms like mobile devices.

In a nutsell, RANSAC homography estimation time depends on the number of iterations and time needed to: 1) fit a homography H_i to a 4 points minimal set and 2) checking for inliers to H_i . However, if most of the random 4 points sets are not geometrically consistent then checking for inliers is not even necesary, they could be rejected very easily.

The code has a heavy impact on estimation time mainly with a high number of outlier matches.

The idea is explained in the paper:

"Speeding-up homography estimation in mobile devices"
Journal of Real-Time Image Processing. 2013. DOI: 10.1007/s11554-012-0314-1
Pablo Márquez-Neila, Javier López-Alberca, José M. Buenaposada, Luis Baumela