Add ast matcher for pattern recognition
Add more generic pattern matching capability
Add generation of classic C loop

* for(int i = x; i < y; i += z)
Add support for real loop with specified step

* If step is computable at compile time, a real loop can be generated.
* It is possible in others case only without omp directive
Improve for generation readability
Merge pull request #289 from pbrunet/real_loop

Real loop