Add typings for module usage

usage/usage-tests.ts

@@ -0,0 +1,19 @@
+/// <reference path="usage.d.ts" />
+/// <reference path="../node/node.d.ts" />
+
+import usage = require('usage');
+
+var pid = process.pid;
+var options = { keepHistory: true };
+
+usage.lookup(pid, function(err, result) {
+  console.log("Usage infos", result);
+});
+
+usage.lookup(pid, options, function (err, result) {
+  console.log("Usage infos with history", result);
+});
+
+usage.clearHistory(pid);
+usage.clearHistory();
+

usage/usage.d.ts

@@ -0,0 +1,28 @@
+// Type definitions for usage
+// Project: https://github.com/arunoda/node-usage
+// Definitions by: Pascal Vomhoff <https://github.com/pvomhoff>
+// Definitions: https://github.com/borisyankov/DefinitelyTyped
+
+declare module "usage" {
+
+  export interface ResultObject {
+    memory:number;
+    memoryInfo: {
+      rss:number;
+      vsize:number;
+    }
+    cpu:number;
+  }
+
+  export interface Options {
+    keepHistory:boolean;
+  }
+
+  export function lookup(pid:number, callback:(err:Error, result:ResultObject) => void);
+  export function lookup(pid:number, options:Options, callback:(err:Error, result:ResultObject) => void);
+
+  //Only availible on linux
+  export function clearHistory(pid?:number);
+
+
+}