doxygen: add groups for all modules

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

src/joystick12/joystick12.h

@@ -29,6 +29,11 @@
 
 namespace upm {
 
+/**
+ * @brief Analog Joystick library
+ * @defgroup joystick libupm-joystick
+ */
+
 /**
  * @brief C++ API for Elecfreaks Joystick v 1.2-1.4 breakout
  *
@@ -36,8 +41,8 @@ namespace upm {
  * button could be treated as normal GPIO, this enables easier
  * interrupt support
  *
+ * @ingroup joystick
  * @snippet joystick12-example.cxx Interesting
- *
  */
 class Joystick12 {
     public: