Add xmake build system support

.gitignore

@@ -16,3 +16,4 @@
 /Android/app/build/
 /Android/build/
 /Android/local.properties
+/.xmake/

GETTING_STARTED.md

@@ -0,0 +1,115 @@
+# Quick Start: Create an EUI-NEO Project
+
+## 1. Create project directory
+
+```sh
+mkdir my-eui-app && cd my-eui-app
+```
+
+## 2. Create `xmake.lua`
+
+```lua
+set_languages("cxx17")
+add_requires("eui-neo")
+
+target("myapp")
+    set_kind("binary")
+    add_files("app.cpp")
+    add_packages("eui-neo")
+```
+
+## 3. Create `app.cpp`
+
+```cpp
+#include "eui_neo.h"
+#include <string>
+
+static std::string g_name;
+static std::string g_greeting;
+
+namespace app {
+
+const DslAppConfig& dslAppConfig() {
+    static const DslAppConfig config = DslAppConfig{}
+        .title("Hello Demo")
+        .windowSize(480, 320);
+    return config;
+}
+
+void compose(eui::Ui& ui, const eui::Screen& screen) {
+    ui.column("root")
+        .size(screen.width, screen.height)
+        .content([&] {
+            ui.text("title")
+                .x(40.0f)
+                .y(32.0f)
+                .text("EUI-NEO Demo")
+                .fontSize(24.0f)
+                .build();
+
+            components::input(ui, "name_input")
+                .x(40.0f)
+                .y(88.0f)
+                .size(400.0f, 40.0f)
+                .placeholder("Enter your name...")
+                .value(g_name)
+                .onChange([](const std::string& value) {
+                    g_name = value;
+                })
+                .build();
+
+            components::button(ui, "say_hello")
+                .x(40.0f)
+                .y(148.0f)
+                .size(160.0f, 44.0f)
+                .text("Say Hello")
+                .onClick([]() {
+                    g_greeting = "Hello, " + g_name + "!";
+                })
+                .build();
+
+            if (!g_greeting.empty()) {
+                ui.text("greeting")
+                    .x(40.0f)
+                    .y(216.0f)
+                    .text(g_greeting)
+                    .fontSize(20.0f)
+                    .build();
+            }
+        })
+        .build();
+}
+
+} // namespace app
+```
+
+## 4. Build and run
+
+```sh
+xmake f -m release -y
+xmake
+xmake run myapp
+```
+
+## Options
+
+```sh
+# SDL2 backend
+xmake f --window_backend=sdl2
+
+# Vulkan renderer
+xmake f --render_backend=vulkan
+
+# Shared library
+xmake f --shared=y
+```
+
+## Included demo
+
+Run the included `hello_demo` example:
+
+```sh
+xmake run hello_demo
+```
+
+Type a name, click "Say Hello", and see the greeting appear.

apps/hello_demo.cpp

@@ -0,0 +1,60 @@
+#include "eui_neo.h"
+#include <string>
+
+static std::string g_name;
+static std::string g_greeting;
+
+namespace app {
+
+const DslAppConfig& dslAppConfig() {
+    static const DslAppConfig config = DslAppConfig{}
+        .title("Hello Demo")
+        .windowSize(480, 320);
+    return config;
+}
+
+void compose(eui::Ui& ui, const eui::Screen& screen) {
+    ui.column("root")
+        .size(screen.width, screen.height)
+        .content([&] {
+            ui.text("title")
+                .x(40.0f)
+                .y(32.0f)
+                .text("EUI-NEO Demo")
+                .fontSize(24.0f)
+                .build();
+
+            components::input(ui, "name_input")
+                .x(40.0f)
+                .y(88.0f)
+                .size(400.0f, 40.0f)
+                .placeholder("Enter your name...")
+                .value(g_name)
+                .onChange([](const std::string& value) {
+                    g_name = value;
+                })
+                .build();
+
+            components::button(ui, "say_hello")
+                .x(40.0f)
+                .y(148.0f)
+                .size(160.0f, 44.0f)
+                .text("Say Hello")
+                .onClick([]() {
+                    g_greeting = "Hello, " + g_name + "!";
+                })
+                .build();
+
+            if (!g_greeting.empty()) {
+                ui.text("greeting")
+                    .x(40.0f)
+                    .y(216.0f)
+                    .text(g_greeting)
+                    .fontSize(20.0f)
+                    .build();
+            }
+        })
+        .build();
+}
+
+} // namespace app