Add a small LED interface and demo app.

app/dartino/main.c

Index: app/dartino/main.c
diff --git a/app/dartino/main.c b/app/dartino/main.c
index 44df2a42bdd733129069e7310d554025dfbfbe71..2ba560af577cf6e144689547ae4eb20a70e50020 100644
--- a/app/dartino/main.c
+++ b/app/dartino/main.c
@@ -15,6 +15,7 @@
 #include <endian.h>
 #include <platform.h>
 #include <dev/display.h>
+#include <dev/gpio.h>
 
 #include <kernel/port.h>
 
@@ -33,6 +34,8 @@
 
 void SensorsInit(void);
 
+int led_get_gpio(int);
+
 enum {
   MODE_RUN,
   MODE_BURN
@@ -78,6 +81,11 @@ DARTINO_EXPORT_TABLE_ENTRY("gfx_flush", gfx_flush)
 DARTINO_EXPORT_TABLE_ENTRY("port_open", port_open)
 DARTINO_EXPORT_TABLE_ENTRY("port_close", port_open)
 DARTINO_EXPORT_TABLE_ENTRY("port_read", port_read)
+#if defined(TARGET_DARTUINOP0)
+DARTINO_EXPORT_TABLE_ENTRY("led_get_gpio", led_get_gpio)
+DARTINO_EXPORT_TABLE_ENTRY("gpio_set", gpio_set)
+DARTINO_EXPORT_TABLE_ENTRY("gpio_get", gpio_get)
+#endif
 DARTINO_EXPORT_TABLE_END
 
 //////////////// Port debug ///////////////////////////////////////////////////