Update api.md

cpp_onnx/api.md

 
+
+```
+初始化程序库
+_RAPIDASRAPI RPASR_HANDLE  RapidAsrInit(const char* szModelDir, int nThread);
+
+
+
+// if not give a fnCallback ,it should be NULL 
+识别内存缓冲区，完整的wav文件数据，包括文件头
+_RAPIDASRAPI RPASR_RESULT	RapidAsrRecogBuffer(RPASR_HANDLE handle, const char* szBuf, int nLen, RPASR_MODE Mode, QM_CALLBACK fnCallback);
+识别内存缓冲区，只包括采样点数据，不包括wav文件头
+_RAPIDASRAPI RPASR_RESULT	RapidAsrRecogPCMBuffer(RPASR_HANDLE handle, const char* szBuf, int nLen, RPASR_MODE Mode, QM_CALLBACK fnCallback);
+识别文件，只包括采样点数据，不包括wav文件头
+_RAPIDASRAPI RPASR_RESULT	RapidAsrRecogPCMFile(RPASR_HANDLE handle, const char* szFileName, RPASR_MODE Mode, QM_CALLBACK fnCallback);
+
+识别音频文件，完整的wav文件数据，包括文件头
+_RAPIDASRAPI RPASR_RESULT	RapidAsrRecogFile(RPASR_HANDLE handle, const char* szWavfile, RPASR_MODE Mode, QM_CALLBACK fnCallback);
+
+获取识别后的文本和相关数据
+_RAPIDASRAPI const char*	RapidAsrGetResult(RPASR_RESULT Result,int nIndex);
+
+获取结果块个数
+_RAPIDASRAPI const int		RapidAsrGetRetNumber(RPASR_RESULT Result);
+
+释放返回的结果块内存
+_RAPIDASRAPI void			RapidAsrFreeResult(RPASR_RESULT Result);
+
+
+使用完成后清理程序库
+_RAPIDASRAPI void			RapidAsrUninit(RPASR_HANDLE Handle);
+
+获取结果块中的数据所表示的音频长度，单位秒
+_RAPIDASRAPI const float	RapidAsrGetRetSnippetTime(RPASR_RESULT Result);
+
+
+```