hmac: add missing version bump and APIChanges entry

Signed-off-by: James Almer <jamrial@gmail.com>
Signed-off-by: Martin Storsjö <martin@martin.st>

doc/APIchanges

@@ -13,6 +13,9 @@ libavutil:     2014-08-09
 
 API changes, most recent first:
 
+2015-07-29 - 7e38340 - lavu 54.16.0 - hmac.h
+  Add AV_HMAC_SHA224 and AV_HMAC_SHA256.
+
 2015-xx-xx - lavc 56.35.0 - avcodec.h
   xxxxxxxxx - Rename CODEC_FLAG* defines to AV_CODEC_FLAG*.
   xxxxxxxxx - Rename CODEC_CAP_* defines to AV_CODEC_CAP_*.

libavutil/version.h

@@ -54,7 +54,7 @@
  */
 
 #define LIBAVUTIL_VERSION_MAJOR 54
-#define LIBAVUTIL_VERSION_MINOR 15
+#define LIBAVUTIL_VERSION_MINOR 16
 #define LIBAVUTIL_VERSION_MICRO  0
 
 #define LIBAVUTIL_VERSION_INT   AV_VERSION_INT(LIBAVUTIL_VERSION_MAJOR, \