Update changelog and readme

Author: mikke89

changelog.md

@@ -9,29 +9,50 @@
 
 ## RmlUi 4.3 (WIP)
 
+
+### Flexbox layout
+
+Support for flexible box layout. [#182](https://github.com/mikke89/RmlUi/issues/182) [#257](https://github.com/mikke89/RmlUi/pull/257)
+
+```css
+display: flex;
+```
+
+See usage examples, differences from CSS, performance tips, and all the details [in the flexbox documentation](https://mikke89.github.io/RmlUiDoc/pages/rcss/flexboxes.html).
+
 ### Elements
 
 - `select` element:
   - Emit `change` event even when the value of the newly selected option is the same.
   - Do not wrap around when using up/down keys on options.
   - Fix unintentional clipping of the scrollbar.
+- `tabset` element: Fix index parameter having no effect in ElementTabSet::SetPanel and ElementTabSet::SetTab. [#237](https://github.com/mikke89/RmlUi/issues/237) [#246](https://github.com/mikke89/RmlUi/pull/246) (thanks @nimble0)
 
-### RCSS Properties
+### RCSS
 
-- Add (non-standard) property value `clip: always` to force clipping to the element, [see `clip` documentation](https://mikke89.github.io/RmlUiDoc/pages/rcss/visual_effects.html#clip). [#235](https://github.com/mikke89/RmlUi/issues/235)
+- Add (non-standard) property value `clip: always` to force clipping to the element, [see `clip` documentation](https://mikke89.github.io/RmlUiDoc/pages/rcss/visual_effects.html#clip). [#235](https://github.com/mikke89/RmlUi/issues/235) [#251](https://github.com/mikke89/RmlUi/pull/251) (thanks @MatthiasJFM)
+- Escape character changed from forward slash to backslash `\`.
 
 ### Layout improvements
 
+- See flexbox layout support above.
 - Fix an issue where some elements could end up rendered at the wrong offset after scrolling. [#230](https://github.com/mikke89/RmlUi/issues/230)
 - Improve behavior for collapsing negative vertical margins.
+- Pixel rounding improvements to the clip region.
+- Performance improvement: Avoid unnecesssary extra layouting step in some situations when scrollbars are added.
 
 ### Samples
 
-- Add clipboard support for X11 samples. [#231](https://github.com/mikke89/RmlUi/pull/231) (thanks @barotto)
+- Add clipboard support to X11 samples. [#231](https://github.com/mikke89/RmlUi/pull/231) (thanks @barotto)
+
+### Lua plugin
+
+- Make Lua plugin API consistently one-indexed instead of zero-indexed. [#237](https://github.com/mikke89/RmlUi/issues/237) [#247](https://github.com/mikke89/RmlUi/pull/247) (thanks @nimble0)
 
 ### Tests
 
 - Visual tests suite: Add ability to overlay the previous reference capture of the test using the shortcut Ctrl+Q.
+- Add support for CSS flexbox tests to the CSS tests converter.
 
 ### Dependencies
 
@@ -42,11 +63,14 @@
 ### Build improvements
 
 - Fix log message format string when compiling in debug mode. [#234](https://github.com/mikke89/RmlUi/pull/234) (thanks @barotto)
+- Avoid enum name collisions with Windows header macros. [#258](https://github.com/mikke89/RmlUi/issues/258)
 
 ### Breaking changes
 
 - The `clip` property is now non-inherited. Users may need to update their RCSS selectors to achieve the same clipping behavior as previously when using this property.
 - Minor changes to the clipping behavior when explicitly using the `clip` property, may lead to different results in some circumstances.
+- RCSS escape character is now `\` instead of `/`.
+- Lua plugin: Some scripts may need to be changed from using zero-based indexing to one-indexing.
 
 
 ## RmlUi 4.2

readme.md

@@ -101,6 +101,7 @@ RmlUi supports most of CSS2 with some CSS3 features such as
 
 - Animations and transitions
 - Transforms (with full interpolation support)
+- Flexbox layout
 - Media queries
 - Border radius
 
@@ -310,6 +311,9 @@ Users can now edit the text field to change the animal. The data bindings ensure
 ![Transform](https://github.com/mikke89/RmlUiDoc/blob/3f319d8464e73b821179ff8d20537013af5b9810/assets/gallery/transform.gif)  
 **Animated transforms (entirely in RCSS)**
 
+![Flexbox](https://github.com/mikke89/RmlUiDoc/blob/4cf0c6ac23b822174e69e5f1413b71254230c619/assets/images/flexbox-example.png)  
+**Flexbox layout**
+
 ![Lottie animation](https://github.com/mikke89/RmlUiDoc/blob/086385e119f0fc6e196229b785e91ee0252fe4b4/assets/gallery/lottie.gif)  
 **Vector animations with the [Lottie plugin](https://mikke89.github.io/RmlUiDoc/pages/cpp_manual/lottie.html)**