feature: IRCv3 `WHOX`

[lrstanley]

✨ Describe the feature you'd like

Ref: IRCv3 WHOX

Introduction

The WHOX extension allows clients to request additional fields in the WHO response (e.g. account name) or omit default fields (e.g. username and hostname).

Once support is added, the IRCv3 Library Support page needs to be updated to include these features.