Telnet represents a connection to a telnet server. The
instance is initially not connected by default; the open()
method must be used to establish a connection. Alternatively, the
host name and optional port number can be passed to the constructor,
to, in which case the connection to the server will be established
before the constructor returns.
Do not reopen an already connected instance.
This class has many read_*() methods. Note that some of them
raise EOFError when the end of the connection is read,
because they can return an empty string for other reasons. See the
individual descriptions below.