Implement channel parting on the channel object

This patch allows the channel to part users from it. This provides the
basics for the future implementation of the PART command.

src/channel.js

@@ -9,6 +9,17 @@ function Channel(name) {
       item.sendRaw(`:${user.nickname} JOIN ${channel.name}`)
     })
   }
+
+  this.part = function(user) {
+      let channel = this
+      let userIndex = this.userlist.indexOf(user)
+      if (userIndex >= 0) {
+          this.userlist.forEach(function(item) {
+              item.sendRaw(`:${user.nickname} PART ${channel.name}`)
+          })
+          this.userlist.splice(index, 1)
+      }
+  }
 }
 
 module.exports = Channel

test/channel.js

@@ -20,4 +20,22 @@ describe('Channel', function () {
             channel.join(mockedUser)
         })
     })
+
+    describe('#part(user)', function () {
+        it("should remove a user from a channel and send a PART command to the user", function (done) {
+            const channel = new Channel("#testchan")
+            let mockedUser = {nickname: "some_nick"}
+            mockedUser.sendRaw = function(data) {
+                // we expect a PART message from our user to the channel (including us)
+                if (data.indexOf("PART") >= 0) {
+                    assert.equal(data, ":some_nick PART #testchan")
+                    done()
+                }
+            }
+            // we can't part a channel without joining it first
+            channel.join(mockedUser)
+
+            channel.part(mockedUser)
+        })
+    })
 })