add couple examples

examples/hash_std.h

@@ -0,0 +1,36 @@
+#ifndef phmap_example_hash_std_
+#define phmap_example_hash_std_
+
+#include <parallel_hashmap/phmap_utils.h>
+
+using std::string;
+
+struct Person
+{
+    bool operator==(const Person &o) const
+    { 
+        return _first == o._first && _last == o._last; 
+    }
+
+    string _first;
+    string _last;
+};
+
+namespace std
+{
+// inject specialization of std::hash for Person into namespace std
+// ----------------------------------------------------------------
+    template<>
+    struct hash<Person>
+    {
+        std::size_t operator()(Person const &p) const
+        {
+            std::size_t seed = 0;
+            phmap::hash_combine(seed, p._first);
+            phmap::hash_combine(seed, p._last);
+            return seed;
+        }
+    };
+}
+
+#endif // phmap_example_hash_std_