Added next/prev trie test

trietestnextprev.json

+{
+    "basic": {
+        "in": [ "cat", "doge", "wallace" ],
+        "tests": [
+            [ "", "", "cat" ],
+            [ "bobo", "", "cat" ],
+            [ "c", "", "cat" ],
+            [ "car", "", "cat" ],
+            [ "cat", "", "doge" ],
+            [ "catering", "cat", "doge" ],
+            [ "d", "cat", "doge" ],
+            [ "doge", "cat", "wallace" ],
+            [ "dogerton", "doge", "wallace" ],
+            [ "w", "doge", "wallace" ],
+            [ "wallace", "doge", "" ],
+            [ "wallace123", "wallace", ""]
+        ]
+    }
+}