Implement addWatcher method to add a watcher to an issue

Add supporting unit test
Update README.md list of what is implemented

Author: Keith Morris

README.md

@@ -107,6 +107,7 @@ JiraApi options:
 *  Issues
   *  Add a new issue
   *  Update an issue
+  *  Add watcher to an issue
   *  Transition an issue
   *  Pulling an issue
   *  Issue linking

lib/jira.js

@@ -1029,6 +1029,53 @@ var JiraApi = exports.JiraApi = function(protocol, host, port, username, passwor
         });
     };
 
+  // ## Add a user as a watcher on an issue ##
+  // ### Takes ###
+  //
+  // *  issueKey: the key of the existing issue
+  // *  username: the jira username to add as a watcher to the issue
+  // *  callback: for when it's done
+  //
+  // ### Returns ###
+  //
+  // *  error: string of the error
+  //
+  //
+  // Empty callback on success
+  /**
+   * Adds a given user as a watcher to the given issue
+   *
+   * @param issueKey
+   * @param username
+   * @param callback
+   */
+    this.addWatcher = function (issueKey, username, callback) {
+
+      var options = {
+        rejectUnauthorized: this.strictSSL,
+        uri: this.makeUri('/issue/' + issueKey + '/watchers'),
+        method: 'POST',
+        followAllRedirects: true,
+        json: true,
+        body: JSON.stringify(username)
+      };
+
+      this.doRequest(options, function (error, response) {
+        if (error) {
+          return callback(error, null);
+        }
+
+        if (response.statusCode === 404) {
+          return callback('Invalid URL');
+        }
+
+        if (response.statusCode !== 204) {
+          return callback(response.statusCode + ': Unable to connect to JIRA to add user as watcher.');
+        }
+        callback();
+      });
+    };
+
     // ## Delete issue to Jira ##
     // ### Takes ###
     //

spec/jira.spec.coffee

@@ -538,6 +538,28 @@ describe "Node Jira Tests", ->
         @jira.request.mostRecentCall.args[1] null, statusCode:201
         expect(@cb).toHaveBeenCalledWith null, "Success"
 
+    it "Adds a watcher to an issue", ->
+        options =
+            rejectUnauthorized: true
+            uri: makeUrl "issue/1/watchers"
+            body: JSON.stringify "testuser"
+            method: 'POST'
+            followAllRedirects: true
+            json: true
+            auth:
+                user: 'test'
+                pass: 'test'
+
+        @jira.addWatcher 1, "testuser", @cb
+        expect(@jira.request).toHaveBeenCalledWith options, jasmine.any(Function)
+
+        @jira.request.mostRecentCall.args[1] null, statusCode: 400
+        expect(@cb).toHaveBeenCalledWith '400: Unable to connect to JIRA to add user as watcher.'
+
+        # Successful Request
+        @jira.request.mostRecentCall.args[1] null, statusCode: 204
+        expect(@cb).toHaveBeenCalledWith
+
     it "Adds a worklog to a project", ->
         options =
             rejectUnauthorized: true