Add documentation for the new IsisPreferences options to specify the use of Embree/Bullet.
Documentation needs to be added about the new optional ShapeModel group in the IsisPreferences file which specifies the use of Embree or Bullet for shapemodel ray-tracing.
Documentation should be added in all the following places:
* In the IsisPreferences file itself (in comments)
* In the IsisPreferences Dictionary webpage https://isis.astrogeology.usgs.gov/documents/PreferenceDictionary/PreferenceDictionary.html
* In the spiceinit documentation (since spiceinit will add the associated keywords to the kernels group.)
#1 Updated by Kristin Berry 4 months ago
During this ticket, I discovered that there was a parameter(which was initially introduced as something user-specifiable in the IsisPreferences file) which is not used and not needed in the ShapeModel class, so, this was removed as well as part of this ticket. Since it was not used, there will be no change in the behavior of ISIS3.
The removed IsisPreferences keyword was
CubeSupported. Right now, DEMs in the ISIS3 Cube format are not supported by the new ShapeModel Bullet or Embree code.