Added NWNX_ON_SPELL_FAILED_{BEFORE|AFTER}

[Cjreek]

Notifies when a spell failed for any reason. The reason is passed to the event handler in the REASON event data and can be one of the following values:

const int NWNX_EVENTS_SPELLFAIL_REASON_CANCELED               = 0;
const int NWNX_EVENTS_SPELLFAIL_REASON_COUNTERSPELL           = 1;
const int NWNX_EVENTS_SPELLFAIL_REASON_ASF                    = 2;
const int NWNX_EVENTS_SPELLFAIL_REASON_SPELLFAILURE           = 3;
const int NWNX_EVENTS_SPELLFAIL_REASON_LOST_TARGET            = 4;
const int NWNX_EVENTS_SPELLFAIL_REASON_SILENCED               = 5;
const int NWNX_EVENTS_SPELLFAIL_REASON_DEFCAST_CONCENTRATION  = 6;
const int NWNX_EVENTS_SPELLFAIL_REASON_ENTANGLE_CONCENTRATION = 7;
const int NWNX_EVENTS_SPELLFAIL_REASON_POLYMORPHED            = 8;
const int NWNX_EVENTS_SPELLFAIL_REASON_CANT_CAST              = 9;
const int NWNX_EVENTS_SPELLFAIL_REASON_CANT_USE_HANDS         = 10;

[Cjreek]

It is done