Misc improvements (#347)

* - Allow for items without namespaces in loot tables

* - Made rolls in loot table required

* - Account for match tag conditions by not requiring item and count

* - Allow forward / in feature (and rule) identifers

* - Added pattern for structure names

* - Change atlas > texture_name to const

* - Allow . in texture entries in atlas files

* - Food nutrition can only be ints

source/behavior/features/features/minecraft.structure_template_feature.json

@@ -11,7 +11,8 @@
     "structure_name": {
       "title": "Structure Name",
       "description": "Reference to the structure to be placed.",
-      "type": "string"
+      "type": "string",
+      "pattern": "^mystructure:(\\w|\/)+"
     },
     "adjustment_radius": {
       "title": "Adjustment Radius",