Implementation of the Window Displacement Iterative Method (WiDIM)

An iterative method performing a simple window shift and widow refinement. Details are in comments of file process.pyx.
These results are 2 weeks old, the code performs validation now. 
![widim-first_results](https://f.cloud.github.com/assets/4153250/488050/d7d2398e-b972-11e2-83ac-15d5afb74489.jpg)


In tools.py: some functions for background and boundary detection using large set of pictures. 

Results of the last version of the code will be shown in next pull request.
A tutorial will be made as soon as possible for how to use WiDIM and background detection.