Documentation and Roster Extension Enhancement

[vsevex]

Documentation:

• Enhanced the documentation for various classes and methods to provide clear explanations and examples.
• Added detailed documentation for the RosterExtension class, its methods, and related functionality.
• Documented the Resource and ResourceShow classes, along with their properties and equality methods.

Roster Extension:

• Implemented the Roster Extension functionality based on XEP-0237.
• Added methods to retrieve and send presence and subscription stanzas.
• Managed user information, subscription requests, and presence updates as per the protocol.
• Implemented IQ handling for roster updates and user management.