add small example program

example/build.sh

@@ -0,0 +1,5 @@
+#!/bin/sh
+
+set -xe
+
+gcc -Wall -Wextra -std=gnu99 $(pkg-config --cflags --libs xcb xcb-xkb cairo pangocairo xkbcommon xkbcommon-x11) -lm main.c -o main

example/main.c

@@ -0,0 +1,58 @@
+#include "pango/pango-font.h"
+#define RAVEN_IMPLEMENTATION
+#include "libraven.h"
+
+typedef struct AppState {
+    PangoFontDescription *desc;
+} AppState;
+
+UINode *main_view_scaffold(UINode *root, AppState *state)
+{
+    {
+        background_node_new(root, UISlate50, 0);
+        UIBoxLayoutNode *layout = box_layout_new(root, UI_DIRECTION_VERTICAL);
+        box_layout_set_margins(layout, 36);
+        layout->gap = 12;
+        layout->justify_secondary_dimension = UI_BOX_LAYOUT_JUSTIFY_CENTER;
+    }
+
+    {
+        UINode *input = (UINode*)text_input_new(root);
+        background_node_new(input, UISlate200, 10);
+        input->width_policy = UI_SIZE_POLICY_STATIC;
+        input->height_policy = UI_SIZE_POLICY_GROW;
+        input->rect.w = 38;
+
+        UIBoxLayoutNode *layout = box_layout_new(input, UI_DIRECTION_HORIZONTAL);
+        layout->justify_secondary_dimension = UI_BOX_LAYOUT_JUSTIFY_CENTER;
+        layout->margin_left = 0;
+
+        UINode *input_text_container = node_new(input, "input_text_container");
+        UITextNode *input_text = text_node_new(input_text_container, state->desc, UINeutral950, NULL);
+        ((UITextInputNode*)input)->text_node = input_text;
+    }
+    
+    return root;
+}
+
+int main(void)
+{
+    UIWindow *window = window_new(800, 600);
+    if (!window) {
+        fprintf(stderr, "err: failed to create window\n");
+        return EXIT_FAILURE;
+    }
+
+    AppState state ={
+        .desc = pango_font_description_from_string("Roboto:size=16")
+    };
+
+    UINode *root = node_new(NULL, "[root]");
+    window_attach_root(window, root);
+    main_view_scaffold(root, &state);
+
+    window_turn(window);
+    window_free(window);
+
+    return 0;
+}