organized level helpers ala mongo driver

src/database/level.js

@@ -69,4 +69,22 @@
 		}
 	};
 
+	var helpers = {};
+
+	helpers.iterator = function(fn, keys, value, callback) {
+		var results = [];
+
+		async.each(keys, function(key, next) {
+			module[fn](key, value, function(err, result) {
+				results.push(result);
+				next();
+			});
+		}, function(err) {
+			callback(err, results);
+		});
+	};
+
+	module.helpers = module.helpers || {};
+	module.helpers.level = helpers;
+
 }(exports));