add air530 gps sleep support

src/gps/Air530GPS.h

@@ -0,0 +1,22 @@
+#pragma once
+
+#include "NMEAGPS.h"
+
+/**
+ * A gps class thatreads from a NMEA GPS stream (and FIXME - eventually keeps the gps powered down except when reading)
+ *
+ * When new data is available it will notify observers.
+ */
+class Air530GPS : public NMEAGPS
+{
+  protected:
+    /// If possible force the GPS into sleep/low power mode
+    virtual void sleep();
+
+    /// wake the GPS into normal operation mode
+    virtual void wake();
+
+  private:
+    /// Send a NMEA cmd with checksum
+    void sendCommand(const char *str);
+};