material.h should include hittable.h #1608
Description
Currently in material.h we have a forward declaration of class hit_record. However, this line is unnecessary because in main.cc, we include hittable.h (where hit_record is defined) before we include material.h. Further, the class declaration is insufficient, as there are multiple member dereferences throughout material.h, which requires the hit_record definition.
The solution to this is to include hittable.h in the beginning of material.h. The current situation likely came about as I wrestled with the potential circular dependency where material classes needed access to hit_record, and hit_record has a shared pointer to a material instance. The current class material declaration at the top of hittable.h should be sufficient to address this.