Add analysis_options, format and fix up (#104)

jsonexample/analysis_options.yaml

@@ -0,0 +1,32 @@
+include: package:pedantic/analysis_options.yaml
+
+analyzer:
+  exclude:
+    - lib/json_serializable/*.g.dart
+  strong-mode:
+    implicit-casts: false
+    implicit-dynamic: false
+
+linter:
+  rules:
+    - avoid_types_on_closure_parameters
+    - avoid_void_async
+    - await_only_futures
+    - camel_case_types
+    - cancel_subscriptions
+    - close_sinks
+    - constant_identifier_names
+    - control_flow_in_finally
+    - empty_statements
+    - hash_and_equals
+    - implementation_imports
+    - non_constant_identifier_names
+    - package_api_docs
+    - package_names
+    - package_prefixed_library_names
+    - test_types_in_equals
+    - throw_in_finally
+    - unnecessary_brace_in_string_interps
+    - unnecessary_getters_setters
+    - unnecessary_new
+    - unnecessary_statements