extract common parser library from socket.io-dart packages for Dart 2

.gitignore

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+# Files and directories created by pub
+.dart_tool/
+.packages
+# Remove the following pattern if you wish to check in your lock file
+pubspec.lock
+
+# Conventional directory for build outputs
+build/
+
+# Directory created by dartdoc
+doc/api/
+
+# JetBrains IDEs
+.idea/
+*.iml
+*.ipr
+*.iws

analysis_options.yaml

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+analyzer:
+#   exclude:
+#     - path/to/excluded/files/**
+
+# Lint rules and documentation, see http://dart-lang.github.io/linter/lints
+linter:
+  rules:
+    - cancel_subscriptions
+    - hash_and_equals
+    - iterable_contains_unrelated_type
+    - list_remove_unrelated_type
+    - test_types_in_equals
+    - unrelated_type_equality_checks
+    - valid_regexps

lib/socket_io_common.dart

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+/**
+ * socket_io_common.dart
+ *
+ * Purpose:
+ *
+ * Description:
+ *
+ * History:
+ *   20/11/2018, Created by jumperchen
+ *
+ * Copyright (C) 2018 Potix Corporation. All Rights Reserved.
+ */
+library socket_io_common;
+
+export 'src/engine/parser/parser.dart';
+export 'src/engine/parser/wtf8.dart';
+export 'src/parser/binary.dart';
+export 'src/parser/parser.dart';
+