Added additional library functionality.

* Extensions.cs:
  Added Range() method.

* IRCClient.cs:
  Added LoggedIn field.
  Added Username field.
  Added MaxBufferSize field.
  Added VerifyLogin() method.
  Added overloaded Connect() method that will also login a user.
  Added SendLine(), ReadLine(), Logout(), and Dispose() methods.
  Implemented Login() method.