This also fixes#194. The backface culling is unintentional because it is not documented anywhere and we can't give the triangle a normal so just assume the general case.
The original implementation had the same mistakes than the ray-sphere
intersection.
Added two new 'out' parameters to return both intersection ponits.
Changed the implementation to the geomethric method.
Changed the original analytic method to a geometrical.
The errors in the original intersection calculation:
The function has a sphere center parameter, but ignores it and assumes
that the sphere is in the origo.
It calculates the length of the ray direction vector, but later on uses
this vector as a unit vector.
The position calculation is simply wrong. It multiplies the direction
vector with the radius of the sphere instead of the calculated
intersection distance.
The quadratic equation solving could be improved too:
There should be an early exit for negative discriminant.
The naive implementation sould be changed to a floating-point
specialized one.
