update API docs about 24bit sample support

TODO

@@ -1,6 +1,5 @@
 New features
 ------------
-- 24 bit sample support
 - Non-realtime MIDI file rendering
 - Sample streaming, load/unload sample on demand
 - Synth sample rate change after initial creation

doc/fluidsynth-v11-devdoc.txt

@@ -113,6 +113,7 @@ Changes in FluidSynth 2.0.0 concerning developers:
 - add file callback struct to _fluid_sfloader_t and expose new_fluid_defsfloader() to enable soundfont loading from memory ( see fluid_sfload_mem.c )
 - add seek support to midi-player, see fluid_player_seek()
 - expose functions to manipulate the ladspa effects unit (see ladspa.h)
+- add 24 bit sample support, see _fluid_sample_t::data24
 
 \section NewIn1_1_9 Whats new in 1.1.9?
 

include/fluidsynth/sfont.h

@@ -298,7 +298,7 @@ struct _fluid_sample_t
   int sampletype;               /**< Specifies the type of this sample as indicated by the #fluid_sample_type enum */
   int valid;                    /**< Should be TRUE if sample data is valid, FALSE otherwise (in which case it will not be synthesized) */
   short* data;                  /**< Pointer to the sample's 16 bit PCM data */
-  char* data24;                 /**< If not NULL, pointer to the sample's contains the least significant byte counterparts to each sample data point */
+  char* data24;                 /**< If not NULL, pointer to the least significant byte counterparts of each sample data point in order to create 24 bit audio samples */
 
   int amplitude_that_reaches_noise_floor_is_valid;      /**< Indicates if \a amplitude_that_reaches_noise_floor is valid (TRUE), set to FALSE initially to calculate. */
   double amplitude_that_reaches_noise_floor;            /**< The amplitude at which the sample's loop will be below the noise floor.  For voice off optimization, calculated automatically. */