Move Telnet handling to separate tiny library

[DavidRieman]

Perhaps WheelMUD.Telnet. It may be nice to have an option to take on as a dependency to get up and running quickly on Telnet for any other highly custom Telnet applications, even for those who don't want to take on any other parts of the framework. This could be a good candidate for experimenting with exposing specific small pieces as independent NuGet packages, too.