Add ".wren" to modules in the embedder.

src/main.c

@@ -52,13 +52,14 @@ static char* readFile(const char* path)
 
 static char* readModule(WrenVM* vm, const char* module)
 {
-  // The module path is relative to the root directory.
+  // The module path is relative to the root directory and with ".wren".
   size_t rootLength = strlen(rootDirectory);
   size_t moduleLength = strlen(module);
-  size_t pathLength = rootLength + moduleLength;
+  size_t pathLength = rootLength + moduleLength + 5;
   char* path = malloc(pathLength + 1);
   memcpy(path, rootDirectory, rootLength);
   memcpy(path + rootLength, module, moduleLength);
+  memcpy(path + rootLength + moduleLength, ".wren", 5);
   path[pathLength] = '\0';
 
   FILE* file = fopen(path, "rb");

src/wren_vm.c

@@ -1174,7 +1174,6 @@ Value wrenImportModule(WrenVM* vm, const char* name)
   return OBJ_VAL(moduleFiber);
 }
 
-
 static void defineMethod(WrenVM* vm, const char* className,
                          const char* methodName, int numParams,
                          WrenForeignMethodFn methodFn, bool isStatic)