doxygen: add groups for all modules

Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>

src/lpd8806/lpd8806.h

@@ -33,11 +33,17 @@
 
 namespace upm {
 
+/**
+ * @brief FastPixel lpd8806 library
+ * @defgroup lpd8806 libupm-lpd8806
+ */
+
 /**
  * @brief C++ API for LPD8806 
  *
  * The FastPixel lpd8806 is an RGB led strip controller.
  *
+ * @ingroup lpd8806
  * @snippet lpd8806-example.cxx Interesting
  * @image html lpd8806.jpeg
  */