Forked from https://github.com/Victorique-GOSICK/Voxel-3D-DDA.
The original owner named it as "Voxel 3D DDA" but actually it is "Fast Voxel Traversal Algorithm" from John Amanatides and Andrew Woo.
May be he/she firstly implemented the DDA but changed to the FVTA instead.
The codes from GOSICK has a problem: when the Ray origin from outside of the grid, he/she snapped the "out of the box" cell into inside the grid.
That made the algorithm become wrongly until the ray really intersect the grid. May be that is his/her intention for his/her work.
So, I updated the code a bit to make it corrected generally.