add lv_components as src/extra and minor fixes

examples/widgets/btn/lv_btn_example_1.c

@@ -0,0 +1,35 @@
+#include "../../../lvgl.h"
+#include <stdio.h>
+#if LV_USE_BTN
+
+static void event_handler(lv_obj_t * obj, lv_event_t event)
+{
+    if(event == LV_EVENT_CLICKED) {
+        printf("Clicked\n");
+    }
+    else if(event == LV_EVENT_VALUE_CHANGED) {
+        printf("Toggled\n");
+    }
+}
+
+void lv_ex_btn_1(void)
+{
+    lv_obj_t * label;
+
+    lv_obj_t * btn1 = lv_btn_create(lv_scr_act(), NULL);
+    lv_obj_add_event_cb(btn1, event_handler, NULL);
+    lv_obj_align(btn1, NULL, LV_ALIGN_CENTER, 0, -40);
+
+    label = lv_label_create(btn1, NULL);
+    lv_label_set_text(label, "Button");
+
+    lv_obj_t * btn2 = lv_btn_create(lv_scr_act(), NULL);
+    lv_obj_add_event_cb(btn2, event_handler, NULL);
+    lv_obj_align(btn2, NULL, LV_ALIGN_CENTER, 0, 40);
+    lv_obj_add_flag(btn2, LV_OBJ_FLAG_CHECKABLE);
+    lv_obj_set_height(btn2, LV_SIZE_AUTO);
+
+    label = lv_label_create(btn2, NULL);
+    lv_label_set_text(label, "Toggle");
+}
+#endif