adding angular limits for the output pointcloud

Hi everybody, here is a little modification of the Velodyne driver: I added the ability to compute and publish only on a defined angular area of the pointcloud.

Motivation:
I'm using a Velodyne 32e for indoor and outdoor navigation. In some configurations I only focus on a part of the output pointcloud from the Velodyne. Select the interesting area at the beginning instead of wasting time doing post-treatment to extract a part of the output pointcloud should save useless computations.

Tests:
I compiled and tested my code with my Velodyne 32e and I don't see any reason that it could fail with another velodyne sensor.

Application:
I'm implementing and testing high speed navigation algorithms for autonomous rovers in unknown outdoor environments. In this situation all the processing must be done on line and I need to save computational ressources in order to run one or many obstacle detection and avoidance algorithms.


Note:
I'm not familiar with github yet. I hope I did everything right, if not I apologize and would be happy to recieve any advice!

Regards
Thomas Solatges