Added a deterministic hash function

CubicNoise/Extensions.cs

@@ -7,6 +7,25 @@ namespace CubicNoise
 {
     public static class Extensions
     {
-        
+        // Source: https://andrewlock.net/why-is-string-gethashcode-different-each-time-i-run-my-program-in-net-core/
+        public static int GetDeterministicHashCode(this string str)
+        {
+            unchecked
+            {
+                var hash1 = (5381 << 16) + 5381;
+                var hash2 = hash1;
+
+                for (var i = 0; i < str.Length; i += 2)
+                {
+                    hash1 = ((hash1 << 5) + hash1) ^ str[i];
+                    if (i == str.Length - 1)
+                        break;
+
+                    hash2 = ((hash2 << 5) + hash2) ^ str[i + 1];
+                }
+
+                return hash1 + (hash2 * 1566083941);
+            }
+        }
     }
 }