add error description to JSONErrors

MVMCore/MVMCore/Models/JSON/JSONHelper.swift

@@ -18,6 +18,30 @@ public enum JSONError: Error {
     case error(message: String)
 }
 
+extension JSONError: LocalizedError, CustomStringConvertible {
+    
+    public var description: String {
+        switch self {
+        case .pathNotFound:
+            return "JSON path not found"
+        case .data(path: let path):
+            return "JSON data in \(path) is corrupt"
+        case .other(error: let error):
+            if let decodingError = error as? DecodingError {
+                // the only way to get the decoding error description and details...
+                return (decodingError as NSError).description
+            }
+            return error.localizedDescription
+        case .error(message: let message):
+            return message
+        }
+    }
+
+    public var errorDescription: String? {
+       return description
+    }
+}
+
 extension JSONDictionary  {
     
     public func toJSONString(options: JSONSerialization.WritingOptions = []) throws -> String {