[mobs] Update (tidy code)

- Put back calc_velocity
- Update mobs mod
- Change the way chicken drop eggs (use throwing-like entities)

mods/mobs/README.txt

@@ -28,6 +28,7 @@ This mod contains the following additions:
 
 Changelog:
 
+1.19- Chickens now drop egg items instead of placing the egg, also throwing eggs result in 1/8 chance of spawning chick
 1.18- Added docile_by_day flag so that monsters will not attack automatically during daylight hours unless hit first
 1.17- Added 'dogshoot' attack type, shoots when out of reach, melee attack when in reach, also api tweaks and self.reach added
 1.16- Mobs follow multiple items now, Npc's can breed