More doc fixes.

In particular we no longer document the default complexity because
we're not guaranteeing to keep the default value constant.  In the
future the default may be lowered in order to keep the default
speed constant.

include/opus_defines.h

@@ -207,20 +207,20 @@ extern "C" {
 /** Configures the encoder's computational complexity.
   * The supported range is 0-10 inclusive with 10 representing the highest complexity.
   * @see OPUS_GET_COMPLEXITY
-  * @param[in] x <tt>opus_int32</tt>: Allowed values: 0-10, inclusive
-  *                                   (default: 10).
+  * @param[in] x <tt>opus_int32</tt>: Allowed values: 0-10, inclusive.
+  *
   * @hideinitializer */
 #define OPUS_SET_COMPLEXITY(x) OPUS_SET_COMPLEXITY_REQUEST, __opus_check_int(x)
 /** Gets the encoder's complexity configuration.
   * @see OPUS_SET_COMPLEXITY
   * @param[out] x <tt>opus_int32 *</tt>: Returns a value in the range 0-10,
-  *                                      inclusive (default: 10).
+  *                                      inclusive.
   * @hideinitializer */
 #define OPUS_GET_COMPLEXITY(x) OPUS_GET_COMPLEXITY_REQUEST, __opus_check_int_ptr(x)
 
 /** Configures the bitrate in the encoder.
   * Rates from 500 to 512000 bits per second are meaningful, as well as the
-  * special values #OPUS_BITRATE_AUTO and #OPUS_BITRATE_MAX.
+  * special values #OPUS_AUTO and #OPUS_BITRATE_MAX.
   * The value #OPUS_BITRATE_MAX can be used to cause the codec to use as much
   * rate as it can, which is useful for controlling the rate by adjusting the
   * output buffer size.
@@ -247,9 +247,8 @@ extern "C" {
   * @see OPUS_SET_VBR_CONSTRAINT
   * @param[in] x <tt>opus_int32</tt>: Allowed values:
   * <dl>
-  * <dt>0</dt><dd>Hard CBR. In the MDCT mode all packets will be the same size.
-  *               In other modes, they will be as close as possible to that
-  *               size.</dd>
+  * <dt>0</dt><dd>Hard CBR. For LPC/hybrid modes at very low bit-rate, this can
+  *               cause noticeable quality degradation.</dd>
   * <dt>1</dt><dd>VBR (default). The exact type of VBR is controlled by
   *               #OPUS_SET_VBR_CONSTRAINT.</dd>
   * </dl>