Create page documenting special event system

[dmethvin]

Docs are here: https://docs.google.com/document/d/1eQG5Mw6TLbO3_Muhlbw5Gu9ZHdLWBE2EcROxtdWCls0/edit?authkey=COe3m_kC&authkey=COe3m_kC

[dmethvin]

A lot of this changed in jQuery 3 and much of it will be removed in jQuery 4 so it would be better not to document it.