scheduleMicrotask utils removed in favor of dart:async

getQueryData wrong arrangment of arguments
Query & Retryer's future property is replaced with Completer
queryFn, fetchFn & fn types corrected
exported all the functions/class/enum  from core (incomplete)
flutter dependency dropped since the core is a Dart package

packages/fl_query/lib/fl_query.dart

@@ -1 +1,4 @@
 library fl_query;
+
+export 'package:fl_query/src/core/core.dart';
+// export 'package:fl_query/src/core/framework.dart';