Provides telnet client functionality.

This class also has, through delegation, all the methods of a socket object
(by default, a TCPSocket, but can be set by the Proxy option to new()). This
provides methods such as close() to end the session and sysread() to read data
directly from the host, instead of via the waitfor() mechanism. Note that if
you do use sysread() directly when in telnet mode, you should probably pass
the output through preprocess() to extract telnet command sequences.