Implement non-direct messages to users

In order to send channel messages, we need to set a different target
than the user himself. This patch adds a new parameter `to` to the
`sendMsg()` function of the user object and allows to provide a string
as target.

This uses by default the user's nickname as target, which makes the
parameter optional and doesn't break the existing interface.

src/user.js

@@ -38,8 +38,8 @@ function User(socket, authenticatedDefault) {
     }
 
 
-    this.sendMsg = function (from, message) {
-        this.sendRaw(`:${from.nickname} PRIVMSG ${this.nickname} :${message}`, "ascii")
+    this.sendMsg = function (from, message, to = this.nickname) {
+        this.sendRaw(`:${from.nickname} PRIVMSG ${to} :${message}`, "ascii")
     }
     this.sendRaw = function(message) {
       this.connection.write(`${message}\r\n`, "ascii")

test/user.js

@@ -16,8 +16,8 @@ describe('User', function () {
         })
     })
 
-    describe('#sendMsg(from, message)', function() {
-        it("should send a message to the user's socket", function (done) {
+    describe('#sendMsg(from, message, to)', function() {
+        it("should send a message to the user's socket with the user himself as target", function (done) {
             let mockedSock = {write: function (data) {
                 assert.equal(data, ":some_nick PRIVMSG some_nick :test message\r\n")
                 done()
@@ -27,6 +27,17 @@ describe('User', function () {
             user.register("some_nick")
             user.sendMsg(user, "test message")
         })
+
+        it("should send a message to the user's socket with a different target", function (done) {
+            let mockedSock = {write: function (data) {
+                assert.equal(data, ":some_nick PRIVMSG #testchan :test message\r\n")
+                done()
+            }}
+            const user = new User(mockedSock, true)
+            user.setNickname("some_nick")
+            user.register("some_nick")
+            user.sendMsg(user, "test message", "#testchan")
+        })
     })
 
     describe('#sendRaw(message)', function() {