doxygen: add groups for all modules

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

src/buzzer/buzzer.h

@@ -36,13 +36,18 @@
 
 namespace upm {
 
+/**
+ * @brief Buzzer library
+ * @defgroup buzzer libupm-buzzer
+ */
+
 /**
  * @brief C++ API for Buzzer component
  *
  * This file defines the Buzzer C++ interface for libbuzzer
  *
+ * @ingroup buzzer
  * @snippet buzzer-sound.cxx Interesting
- *
  */
 class Buzzer {
     public: