Update readme

Signed-off-by: Jack Cherng <jfcherng@gmail.com>

Author: jfcherng

README.md

@@ -174,7 +174,7 @@ $result = $diff->render($renderer);
 
 ## Renderer: JSON
 
-<details><summary>Click to expand the result</summary>
+<details><summary>Click to expand</summary>
 
 ```javascript
 [
@@ -322,20 +322,41 @@ $result = $diff->render($renderer);
 # Upgrading
 
 
-## From v2 to v3
+<details><summary>From v2 to v3</summary>
 
 - `$diffOptions` removes: `charLevelDiff` and `separateBlock`.
 - `$templateOptions` adds: `detailLevel` (similar to `charLevelDiff`, read docs) and `separateBlock` (exact the same one in `$diffOptions`).
 - `Jfcherng\Diff\Diff`'s `$a` (`$old`), `$b` (`$new`) are required in `__construct()`. (You may pass two empty arrays if you do not want to do anything at that moment.)
 - The look of "skipped" block in HTML renderers (`SideBySide` and `Inline`) have been changed. (You may have to tweak your CSS.)
 
+</details>
 
-## From v3 to v4
+<details><summary>From v3 to v4</summary>
 
 - `Jfcherng\Diff\Utility\SequenceMatcher` becomes [a new package](https://packagist.org/packages/jfcherng/php-sequence-matcher) by the namespace of `Jfcherng\Diff\SequenceMatcher`.
 - Factories under `Jfcherng\Diff\Utility\` are moved to `Jfcherng\Diff\Factory\`. For example, `Jfcherng\Diff\Utility\RendererFactory` is now `Jfcherng\Diff\Factory\RendererFactory`.
 - Non-abstract classes are no longer inheritable as they are added with `final` keywords. (This allows me to do more internal changes without causing possible BC breaks.)
 
+</details>
+
+<details><summary>From v4 to v5</summary>
+
+- Names involving `a, b`, `from, to`, `base, changed` have been renamed to `old, new` for consistency.
+  Here's some examples:
+
+  - `Diff::setA()` becomes `Diff::setOld()`.
+  - `Diff::setB()` becomes `Diff::setNew()`.
+  - `Diff::setAB()` becomes `Diff::setOldNew()`.
+  - `base`, `changed` keys in the result of the `Json` renderer have become `old`, `new`.
+
+- In the result of HTML renderers, classes of rows of line numbers has been changed.
+  You may have to change your CSS if you have some customized things depend on these.
+
+  - `<th class="f-num">` (from-number) becomes `<th class="n-new">` (number-new).
+  - `<th class="t-num">` (to-number) becomes `<th class="n-old">` (number-old).
+
+</details>
+
 
 # Acknowledgment