Revving format to 2 with smaller string encoding.

example/lib/main.dart

@@ -44,7 +44,7 @@ class _MyHomePageState extends State<MyHomePage> {
 
     // Load the animation file from the bundle, note that you could also
     // download this. The RiveFile just expects a list of bytes.
-    rootBundle.load('assets/colors_juice.riv').then(
+    rootBundle.load('assets/teeny_tiny.riv').then(
       (data) async {
         var file = RiveFile();
         // Load the RiveFile from the binary data.
@@ -56,7 +56,7 @@ class _MyHomePageState extends State<MyHomePage> {
           // Add a controller to play back a known animation on the main/default
           // artboard.We store a reference to it so we can toggle playback.
           artboard.addController(
-            _controller = SimpleAnimation('walk'),
+            _controller = SimpleAnimation('idle'),
           );
           setState(() => _riveArtboard = artboard);
         }

lib/src/core/field_types/core_string_type.dart

@@ -3,7 +3,8 @@ import 'package:rive/src/utilities/binary_buffer/binary_reader.dart';
 
 class CoreStringType extends CoreFieldType<String> {
   @override
-  String deserialize(BinaryReader reader) => reader.readString();
+  String deserialize(BinaryReader reader) =>
+      reader.readString(explicitLength: false);
 
   @override
   String lerp(String from, String to, double f) => from;

lib/src/rive_core/runtime/runtime_header.dart

@@ -4,7 +4,7 @@ import 'package:rive/src/utilities/binary_buffer/binary_reader.dart';
 import 'exceptions/rive_format_error_exception.dart';
 
 class RuntimeHeader {
-  static const int majorVersion = 1;
+  static const int majorVersion = 2;
   static const int minorVersion = 0;
   static const String fingerprint = 'RIVE';
   final int ownerId;

lib/src/utilities/binary_buffer/binary_reader.dart

@@ -115,8 +115,8 @@ class BinaryReader {
   /// Read a string encoded into the stream. Strings are encoded with a varuint
   /// integer length written first followed by length number of utf8 encoded
   /// bytes.
-  String readString() {
+  String readString({bool explicitLength = true}) {
-    int length = readVarUint();
+    int length = explicitLength ? readVarUint() : buffer.lengthInBytes;
     String value = _utf8Decoder.convert(Uint8List.view(
         buffer.buffer, buffer.offsetInBytes + _readIndex, length));
     _readIndex += length;

lib/src/utilities/binary_buffer/binary_writer.dart

@@ -151,9 +151,11 @@ class BinaryWriter {
   /// Encode a string into the buffer. Strings are encoded with a varuint
   /// integer length written first followed by length number of utf8 encoded
   /// bytes.
-  void writeString(String value) {
+  void writeString(String value, {bool explicitLength = true}) {
     var list = _utf8Encoder.convert(value);
-    writeVarUint(list.length);
+    if (explicitLength) {
+      writeVarUint(list.length);
+    }
     write(list);
   }