Update to the mapping guide about coordinate system convention

[Scheggetta]

After mapping, the user has to replace the origin attribute with [0, 0, 0]. This new convention will allow greater code clarity and faster execution of the particle_filter and range_libc library.

Now RViz follows this easy human convention:

The origin is in the bottom left of the image. 0 rad heading lies along the x axis, positive heading rotates towards the positive y axis.

[Scheggetta]

This is suspended since it has been discovered that also in the original range_libc library the cddt ray casting variant crashes.