Npc retreat2 (#30)

* Expose NPC AI consts to options

I will probably need a little help with this

* Restore 'regroup on player'

Now it won't kick in if the NPC is already close to you

* Remove unnecessary messages

* Update data/core/game_balance.json

data/core/game_balance.json

@@ -107,7 +107,7 @@
   {
     "type": "EXTERNAL_OPTION",
     "name": "NPC_COWARDICE_MODIFIER",
-    "info": "This is a multiplier applied to an NPC's assessment of overall threat. The lower it is, the less likely they are to run away from their problems.  It has been tested between 0.1 and 0.5 pretty effectively.",
+    "info": "This is a multiplier applied to an NPC's assessment of overall threat.  The lower it is, the less likely they are to run away from their problems.  It has been tested between 0.1 and 0.5 pretty effectively.",
     "stype": "float",
     "value": 0.5
   },