Update/extend documentation of PrimitiveID class
This merge request
- re-writes and extends documentation text of
PrimitiveID
class - adds three images to better explain the format of the bit pattern
- groups documentation of
PrimitiveID::asIntArray()
methods together - updates meta-data in
PrimitiveID.hpp
- relocates PrimitiveID.hpp to the sub-folder
src/hyteg/primitives