add config.setDefaultValue

lib/ace/config.js

@@ -258,4 +258,17 @@ exports.resetOptions = function(obj) {
     });
 };
 
+exports.setDefaultValue = function(path, name, value) {
+    var opts = defaultOptions[path] || (defaultOptions[path] = {});
+    if (typeof name == "string") {
+        if (opts[name])
+            opts[name].value = value;
+    } else {
+        Object.keys(name).forEach(function(key) {
+            if (opts[key])
+                opts[key].value = name[key];
+        });
+    }
+};
+
 });