AP_ExternalControl: external control library for MAVLink,lua and DDS

Signed-off-by: Ryan Friedman <ryanfriedman5410+github@gmail.com>
Co-authored-by: Andrew Tridgell <tridge60@gmail.com>

libraries/AP_ExternalControl/AP_ExternalControl.cpp

@@ -0,0 +1,24 @@
+#include "AP_ExternalControl.h"
+
+#if AP_EXTERNAL_CONTROL_ENABLED
+
+// singleton instance
+AP_ExternalControl *AP_ExternalControl::singleton;
+
+AP_ExternalControl::AP_ExternalControl()
+{
+    singleton = this;
+}
+
+
+namespace AP
+{
+
+AP_ExternalControl *externalcontrol()
+{
+    return AP_ExternalControl::get_singleton();
+}
+
+};
+
+#endif // AP_EXTERNAL_CONTROL_ENABLED