Move array hasher back to header file

Since it is a template function it needs to be in the header...

surfseg/include/util.h

@@ -16,10 +16,20 @@ namespace std {
 
     template <size_t N>
     struct hash<std::array<int, N>> {
-        size_t operator()(const std::array<int, N>& key) const noexcept;
+        size_t operator()(const std::array<int, N>& key) const noexcept
+        {
+            // Code from https://codereview.stackexchange.com/q/171999
+            static std::hash<int> hasher;
+            size_t result = 0;
+            for (int k : key) {
+                result = result * 31 + hasher(k);
+            }
+            return result;
+        }
     };
 } // std
 
+
 void graphErrFunc(const char *msg);
 
 template <class Ty>

surfseg/src/util.cpp

@@ -8,18 +8,6 @@ size_t std::hash<std::pair<int, int>>::operator()(const std::pair<int, int>& key
     return hasher(tohash);
 }
 
-template <size_t N>
-size_t std::hash<std::array<int, N>>::operator()(const std::array<int, N>& key) const noexcept
-{
-    // Code from https://codereview.stackexchange.com/q/171999
-    static std::hash<int> hasher;
-    size_t result = 0;
-    for (int k : key) {
-        result = result * 31 + hasher(k);
-    }
-    return result;
-}
-
 void graphErrFunc(const char *msg)
 {
 	// To avoid crashing the program we throw an exception here since Graph will otherwise call exit(1)