Implement Telnet Linemode and SGA Option

[mystiker]

Description

This change adds two new features to all Telnet option handlers: getPreviousNegotiation and isDynamic.

The getPreviousNegotiation function allows option handlers to access the previous negotiation result, enabling more flexible and dynamic negotiation of Telnet options between the client and server.

The isDynamic property indicates whether an option handler is dynamic or not. A dynamic option handler can change its negotiation even after the first negotiation during runtime, while a non-dynamic option handler always sticks to its first decision. When isDynamic is set to true, the option handler can change its negotiation based on the previous negotiation results.

Changes

• The getPreviousNegotiation function was added to allow option handlers to access the previous negotiation result.
• The isDynamic property was added to indicate whether an option handler is dynamic or not.
• The handleLinemodeOption function was updated to support the new features.
• Support for the Telnet option LINEMODE (34) was added, allowing negotiation line mode with the server.
• Support for the Telnet option SGA (3) was added, allowing to suppress go-ahead messages from the server.

Fixes #114
Fixes #115