[doc] Put CRC-16 and generic CRC code in one Doxygen module

.. and add missing API documentation bits

Change-Id: I67119894bcbf8c779426a0272bae4c5ce1fbd1ed
diff --git a/src/crcXXgen.c.tpl b/src/crcXXgen.c.tpl
index e92a538..befba4d 100644
--- a/src/crcXXgen.c.tpl
+++ b/src/crcXXgen.c.tpl
@@ -20,7 +20,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-/*! \addtogroup crcgen
+/*! \addtogroup crc
  *  @{
  *  Osmocom generic CRC routines (for max XX bits poly).
  *