Applied o11c's suggested changes from code review.
Added generic aiflags to mob spawns

This is accomplished with an extra field in the line containing
single characters that equate to various flags. The guard flag
is 'g'

Ex: Spawn for FireSkull in North Mines with guard aiflag enabled:
018-3.gat,98,75,1,2|monster|FireSkull|1023,1,120000,30000,Mob018-3::On1023,g

If this code ends up live the converter and wiki will be updated.