Add documentation on event variable names to nwnx_events.nss

[zunath]

No description provided.

[Liareth]

It might be better to change the format of this? It's grouped under 'item events etc' in the format that the code is, but not all items events necessarily have the same event data. The General Notes: is a bit redundant too.

Maybe a slight tweak to make it more readable, like this? (just an example)

//    NWNX_ON_ADD_ASSOCIATE_AFTER
//    NWNX_ON_REMOVE_ASSOCIATE_BEFORE
//    NWNX_ON_REMOVE_ASSOCIATE_AFTER
//     
//    Usage:
//      OBJECT_SELF = The owner of the associate
//
//    Event data:
//      Variable Name           Type                Notes
//      ASSOCIATE_OBJECT_ID     object              Convert to object with NWNX_Object_StringToObject
//
//    NWNX_ON_ENTER_STEALTH_BEFORE
//    NWNX_ON_ENTER_STEALTH_AFTER
//    NWNX_ON_EXIT_STEALTH_BEFORE
//    NWNX_ON_EXIT_STEALTH_AFTER
//
//    Usage:
//      OBJECT_SELF = The creature entering or leaving stealth.
//
//

[zunath]

I'll have to get back into this one at a later date. Don't have the time right now. I'll go ahead and close this PR for now