- Move overmap defines to _defines folder. Rename old file to turfs.dm since that is what it contains.
- Definition of overmap event objects and the overmap event handler.
- Upgrades to SSevents and SSskybox to tie in the overmap events.
- Enhancement to /datum/event itself to support affecting_z and victim ship.
- Upgrade to the five event types used on the overmap to support new vars.
- Upgrade to dust and meteor spawning code to support targeting z-levels.
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