add ui module

demo/ui_demo.fnl

@@ -0,0 +1,20 @@
+(local pxl8 (require :pxl8))
+
+(var button-clicks 0)
+
+(global init (fn []
+  (pxl8.load_palette "palettes/gruvbox.ase")))
+
+(global update (fn [_dt]))
+
+(global frame (fn []
+  (pxl8.clr 1)
+
+  (when pxl8.ui
+    (when (pxl8.ui_window_begin "UI Demo" 20 20 280 150)
+      (pxl8.ui_layout_row 1 0 0)
+      (pxl8.ui_label "Welcome to some window UI!")
+      (pxl8.ui_label (.. "Clicks: " button-clicks))
+      (when (pxl8.ui_button "Click me!")
+        (set button-clicks (+ button-clicks 1)))
+      (pxl8.ui_window_end)))))