Adds support for optional formes in encounter schema

encounters.schema.json

@@ -42,6 +42,20 @@
           },
           "maximumlvl": {
             "type": "integer"
+          },
+          "formes": {
+            "type": "array",
+            "items": {
+              "type": "object",
+              "properties": {
+                "forme": {
+                  "type": "string"
+                },
+                "chance": {
+                  "type": "integer"
+                }
+              }
+            }
           }
         }
       }