Add 3.0.3 entry

NEWS.md

@@ -0,0 +1,44 @@
+# News
+
+## 3.0.3 - 2022-12-08
+
+### Improvements
+
+  * Improved documents.
+    [[GitHub#33](https://github.com/ruby/stringio/pull/33)]
+    [[GitHub#34](https://github.com/ruby/stringio/pull/34)]
+    [[GitHub#35](https://github.com/ruby/stringio/pull/35)]
+    [[GitHub#36](https://github.com/ruby/stringio/pull/36)]
+    [[GitHub#37](https://github.com/ruby/stringio/pull/37)]
+    [Patch by Burdette Lamar]
+
+### Fixes
+
+  * Fixed a bug that large `StringIO#ungetc`/`StringIO#ungetbyte`
+    break internal buffer.
+
+  * Fixed a bug that `StringIO#each("2+ character", chomp: true)` cause
+    infinite loop.
+    [[Bug #18769](https://bugs.ruby-lang.org/issues/18769)]
+
+  * Fixed a bug that `StringIO#each(nil, chomp: true)` chomps.
+    [[Bug #18770](https://bugs.ruby-lang.org/issues/18770)]
+
+  * Fixed a bug that `StringIO#each("", chomp: true)` isn't compatible
+    with `IO#each("", chomp: true)`.
+    [[Bug #18768](https://bugs.ruby-lang.org/issues/18768)]
+
+  * Fixed a bug that `StringIO#set_encoding` doesn't accept external
+    and internal encodings pairo.
+    [[GitHub#16](https://github.com/ruby/stringio/issues/16)]
+    [Reported by Kenta Murata]
+
+  * Fixed a bug that `StringIO#truncate` isn't compatible with
+    `File#truncate`.
+
+### Thanks
+
+  * Kenta Murata
+
+  * Burdette Lamar
+