bind socket on worker thread for thread ownership
pt: set correct focal length from camera fov

Issue: #96

Having user-supplied camera fov, we can prevent yaw and pitch occuring
by itself when moving horizontally and vertically.

Note PointExtractor::extract_points(Mat& frame) should enable same value
for fx and fy:

			c[0] =  (mx/m - W/2)/W;
			c[1] = -(my/m - H/2)/W;