Add type signature for node events module

lib/node.js

@@ -339,12 +339,27 @@ declare module "domain" {
   declare function create(): domain$Domain;
 }
 
-type events$EventEmitter = {
-
-};
+// TODO: This is copypast of the EventEmitter class signature exported from the
+//       `events` module. The only reason this exists is because other module
+//       interface definitions need to reference this type structure -- but
+//       referencing type structures defined in other modules isn't possible at
+//       the time of this writing.
+declare class events$EventEmitter {
+  static listenerCount(emitter: events$EventEmitter, event: string): number;
+
+  addListener(event: string, listener: Function): events$EventEmitter;
+  emit(event: string, ...args:Array): boolean;
+  listeners(event: string): Array<Function>;
+  on(event: string, listener: Function): events$EventEmitter;
+  once(event: string, listener: Function): events$EventEmitter;
+  removeAllListeners(events?: Array<string>): events$EventEmitter;
+  removeListener(event: string, listener: Function): events$EventEmitter;
+  setMaxListeners(n: number): void;
+}
 
 declare module "events" {
-  // TODO
+  // TODO: See the comment above the events$EventEmitter declaration
+  declare class EventEmitter extends events$EventEmitter {}
 }
 
 declare module "fs" {