DLS method for solving PnP task + Documentation update

Added DLS method for solving PnP task in the calib3d module. 

Method based on the paper of Joel A. Hesch and Stergios I. Roumeliotis. "A Direct Least-Squares (DLS) Method for PnP".
ok. What about in modules/calib3d/include/opencv2/calib3d/calib3d_c.h  ?