point: add trivial std::hash specialisation

point.hpp

@@ -82,6 +82,24 @@ namespace util {
     typedef point<2,size_t> point2u;
 }
 
+#include <functional>
+
+namespace std {
+    template <>
+    template <size_t S, typename T>
+    struct hash<util::point<S,T>> {
+        size_t operator() (const util::point<S,T> &p) const {
+            std::hash<T> h;
+
+            size_t k = 0;
+            for (size_t i = 0; i < S; ++i)
+                k = h (p.data[i] ^ k);
+
+            return k;
+        }
+    };
+}
+
 #include "point.ipp"
 
 #endif // __UTIL_POINT_HPP