Unify the amplifier API into a single group

doc/index.doxygen

@@ -101,4 +101,5 @@ of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
  *  \defgroup rotator Rotator API
  *  \defgroup utilities Utility Routines API
  *  \defgroup rig_internal Rig Internal API
+ *  \defgroup amplifier Amplifier API
  */

include/hamlib/amplifier.h

@@ -26,7 +26,7 @@
 #include <hamlib/amplist.h>
 
 /**
- * \addtogroup amp
+ * \addtogroup amplifier
  * @{
  */
 

src/extamp.c

@@ -22,7 +22,7 @@
  */
 
 /**
- * \addtogroup amp
+ * \addtogroup amplifier
  * @{
  */