Init rate limiter

lib/src/rate_limiter.dart

@@ -0,0 +1,14 @@
+import 'package:angel_framework/angel_framework.dart';
+
+/// A base class that facilitates rate limiting API's or endpoints,
+/// typically to prevent spam and abuse.
+abstract class RateLimiter {
+  /// The maximum number of requests allowed within the given [window].
+  final int maxRequestsPerWindow;
+
+  /// The amount of time, during which, a user is not allowed to send
+  /// more than [maxRequestsPerWindow].
+  final Duration window;
+
+  RateLimiter(this.maxRequestsPerWindow, this.window);
+}