hashmap: Support strings by default

String storage requires different mechanisms than simple integer
storage, so the hashmap must behave differently when dealing with
strings and simple pointer comparisons.

This makes the default behaviour string-based, meaning integer
based keys should use the puti, geti, deli methods. These should
be the main key types that need to be supported within the context
of buxton.

Signed-off-by: Michael Ikey Doherty <michael.i.doherty@intel.com>