vp8[cd]x.h: document vpx_codec_vp[89]_[cd]x*

+ mark the _algo variables as deprecated.
this quiets some doxygen warnings

Bug: webm:1752
Change-Id: I53b9b796c3d8fef5c713ee4278641198f95b5864

vpx/vp8cx.h

@@ -33,7 +33,15 @@ extern "C" {
  * This interface provides the capability to encode raw VP8 streams.
  * @{
  */
+
+/*!\brief A single instance of the VP8 encoder.
+ *\deprecated This access mechanism is provided for backwards compatibility;
+ * prefer vpx_codec_vp8_cx().
+ */
 extern vpx_codec_iface_t vpx_codec_vp8_cx_algo;
+
+/*!\brief The interface to the VP8 encoder.
+ */
 extern vpx_codec_iface_t *vpx_codec_vp8_cx(void);
 /*!@} - end algorithm interface member group*/
 
@@ -42,7 +50,15 @@ extern vpx_codec_iface_t *vpx_codec_vp8_cx(void);
  * This interface provides the capability to encode raw VP9 streams.
  * @{
  */
+
+/*!\brief A single instance of the VP9 encoder.
+ *\deprecated This access mechanism is provided for backwards compatibility;
+ * prefer vpx_codec_vp9_cx().
+ */
 extern vpx_codec_iface_t vpx_codec_vp9_cx_algo;
+
+/*!\brief The interface to the VP9 encoder.
+ */
 extern vpx_codec_iface_t *vpx_codec_vp9_cx(void);
 /*!@} - end algorithm interface member group*/
 

vpx/vp8dx.h

@@ -32,7 +32,15 @@ extern "C" {
  * This interface provides the capability to decode VP8 streams.
  * @{
  */
+
+/*!\brief A single instance of the VP8 decoder.
+ *\deprecated This access mechanism is provided for backwards compatibility;
+ * prefer vpx_codec_vp8_dx().
+ */
 extern vpx_codec_iface_t vpx_codec_vp8_dx_algo;
+
+/*!\brief The interface to the VP8 decoder.
+ */
 extern vpx_codec_iface_t *vpx_codec_vp8_dx(void);
 /*!@} - end algorithm interface member group*/
 
@@ -41,7 +49,15 @@ extern vpx_codec_iface_t *vpx_codec_vp8_dx(void);
  * This interface provides the capability to decode VP9 streams.
  * @{
  */
+
+/*!\brief A single instance of the VP9 decoder.
+ *\deprecated This access mechanism is provided for backwards compatibility;
+ * prefer vpx_codec_vp9_dx().
+ */
 extern vpx_codec_iface_t vpx_codec_vp9_dx_algo;
+
+/*!\brief The interface to the VP9 decoder.
+ */
 extern vpx_codec_iface_t *vpx_codec_vp9_dx(void);
 /*!@} - end algorithm interface member group*/