add user api

lib/api/index.js

@@ -2,7 +2,8 @@ var api = {
     tag: require("./tag"),
     metric: require("./metric"),
     event: require("./event"),
-    serviceCheck: require("./serviceCheck")
+    serviceCheck: require("./serviceCheck"),
+    user: require("./user")
 };
 
 module.exports = function(obj){

lib/api/user.js

@@ -0,0 +1,33 @@
+var client = require("../client");
+
+/*section: user
+ *comment: invite users via e-mail
+ *params:
+ *  emails: an array of email addresses to send invites to
+ *  callback: function(err, res)
+ *example: |
+ *  ```javascript
+ *  var dogapi = require("dogapi");
+ *  var options = {
+ *    api_key: "api_key",
+ *    app_key: "app_key"
+ *  };
+ *  dogapi.initialize(options);
+ *  var emails = ["me@domain.com", "you@domain.com"];
+ *  dogapi.user.invite(emails, fuction(err, res){
+ *    console.dir(res):
+ *  });
+ *  ```
+ */
+function invite(emails, callback){
+    var params = {
+        body: {
+            emails: emails
+        }
+    };
+    client.request("POST", "/invite_users", params, callback);
+};
+
+module.exports = {
+    invite: invite
+};