move terminal_isolate to keep web support

example/lib/main.dart

@@ -3,6 +3,7 @@ import 'dart:async';
 import 'package:flutter/material.dart';
 import 'package:xterm/flutter.dart';
 import 'package:xterm/xterm.dart';
+import 'package:xterm/isolate.dart';
 
 void main() {
   runApp(MyApp());

lib/isolate.dart

@@ -0,0 +1 @@
+export 'terminal/terminal_isolate.dart';

lib/terminal/terminal_backend.dart

@@ -1,5 +1,3 @@
-import 'package:xterm/terminal/terminal_isolate.dart';
-
 /// interface for every Terminal backend
 abstract class TerminalBackend {
   /// initializes the backend

lib/xterm.dart

@@ -1,7 +1,6 @@
 library xterm;
 
 export 'terminal/terminal.dart';
-export 'terminal/terminal_isolate.dart';
 export 'terminal/terminal_backend.dart';
 export 'terminal/terminal_ui_interaction.dart';
 export 'terminal/platform.dart';