Release 2.1.0

Add index-returning string match methods to JSON-reader.

Release 2.0.0

Update to new language version (3.0+) and lints.

Add class modifiers on classes. Most `final`.

Change return type of some `void` methods to `Null`,
to allow chaining them after, for example, `tryString() ??`,
as a default fallback.

Optimize whitespace skipping.

Make `ByteReader` and `StringReader` sources more in sync.

Accept Dart 3.0 SDK, tweaks in byte_writer.

Clean up example test.