Add Changelog. (#213)

- Increase version to 0.9
- Add a changelog.

From now one. Developpement happens on the `dev` branch.

See: https://github.com/ArthurSonzogni/FTXUI/discussions/207

CHANGELOG.md

+# Changelog
+
+## 0.9 (2021-09-26)
+
+The initial release where changelog where written.
+
+This version includes:
+
+### screen
+- Style:
+  - Bold.
+  - Blink.
+  - Dim.
+  - Inverted.
+  - Underlined.
+  - Foreground color.
+  - Background color.
+- Support for UTF8 unicode.
+  - Full wide character: 测试.
+  - Combining characters: a⃒
+- A Stencil buffer.
+- Automatically merge box drawing characters.
+- Detect terminal dimension.
+
+### DOM
+
+- Element:
+  - `text` & `vtext`
+  - `separator` and 5 variations.
+  - `gauge`
+  - `border` and 6 variations.
+  - `window`
+  - `spinner`
+  - `paragraph` and `hflow`.
+
+- Layout:
+  - `hbox`
+  - `vbox`
+  - `dbox`
+  - `gridbox`
+  - `frame`: Drawing inside a virtual area, potentially larger than the real
+             one.
+  - `focus`, `select`: scroll the inner view of a frame, to be in view.
+  - `flex` & 8 variations. `filler`
+  
+- Decorators:
+  - `bold`
+  - `dim`
+  - `inverted`
+  - `blink`
+  - `color`
+  - `bgcolor`
+  - `clearunder`
+
+### Component
+
+- Container:
+  - `Container::Vertical`
+  - `Container::Horizontal`
+  - `Container::Tab`
+- `Button`
+- `Checkbox`
+- `Input`
+- `Menu`
+- `MenuEntry`
+- `Radiobox`
+- `Toggle`
+- `Slider`
+- `Renderer` & variations
+- `CatchEvent`
+
+### MISC
+
+- Fuzzer
+- Tests using gtest.
+- Doxygen documentation
+- IWYU
+- 52 examples.
+- Support for WebAssembly.
+- Support for Window and fallback for broken terminal.

CMakeLists.txt

@@ -4,7 +4,7 @@ include(cmake/ftxui_git_version.cmake)
 
 project(ftxui
   LANGUAGES CXX
-  VERSION 0.8.${git_version}
+  VERSION 0.9.${git_version}
 )
 
 option(FTXUI_BUILD_DOCS "Set to ON to build tests" ON)