Also, removed the one from modules/python/src2/cv.py and cleared its
executable bit, since it's not a script.

e.g. <opencv2/core/core.hpp> become <opencv2/core.hpp>

Also renamed <opencv2/core/opengl_interop.hpp> to <opencv2/core/opengl.hpp>

a lot of small corrections to bring down the number of undocumented functions, reported by the script; added em.cpp sample

started work on API & doc synchronization (in particular, Mat& => Input/OutputArray in the descriptions)