core: Add hashing functor for creating hash of a Ptr
This change introduces an std::hash functor class which takes
Ptr and return an std::size_t value.
The hash is calculated from using std::hash of PeekPointer ()
function. PeekPointer () directly doesn't work as the hash
for the pointer.
Credits: Peter D. Barnes, Jr barnes26@llnl.gov
Signed-off-by: Ameya Deshpande ameyanrd@outlook.com
Edited by Ameya Deshpande