Use ZSTD Error codes, improve explanation of ZSTD_loadCEntropy() and ZSTD_loadDEntropy()

lib/compress/zstd_compress_internal.h

@@ -931,13 +931,13 @@ MEM_STATIC void ZSTD_debugTable(const U32* table, U32 max)
 }
 #endif
 /* ===============================================================
- * Public declarations
+ * Shared internal declarations
  * These prototypes may be called from sources not in lib/compress
  * =============================================================== */
 
 /* ZSTD_loadCEntropy() :
  * dict : must point at beginning of a valid zstd dictionary.
- * return : size of entropy tables read */
+ * return : size of dictionary header (size of magic number + dict ID + entropy tables) */
 size_t ZSTD_loadCEntropy(ZSTD_compressedBlockState_t* bs, void* workspace,
                          short* offcodeNCount, unsigned* offcodeMaxValue,
                          const void* const dict, size_t dictSize);