Create an error context API.

This will allow the espeak-ng methods to provide more context
information for the errors that can then be used in things like
GUI applications.

src/include/espeak-ng/espeak_ng.h

 	ENOUTPUT_MODE_SPEAK_AUDIO = 0x0002,
 } espeak_ng_OUTPUT_MODE;
 
+typedef struct espeak_ng_ERROR_CONTEXT_ *espeak_ng_ERROR_CONTEXT;
+
+ESPEAK_NG_API void
+espeak_ng_ClearErrorContext(espeak_ng_ERROR_CONTEXT *context);
+
 ESPEAK_NG_API void
 espeak_ng_GetStatusCodeMessage(espeak_ng_STATUS status,
                                char *buffer,

src/libespeak-ng/error.c

 #include <stdint.h>
 #endif
 #include <string.h>
+#include <malloc.h>
 
 #include "espeak_ng.h"
 
+#include "error.h"
 #include "speech.h"
 #include "phoneme.h"
 #include "synthesize.h"
 
+espeak_ng_STATUS create_file_error_context(espeak_ng_ERROR_CONTEXT *context, espeak_ng_STATUS status, const char *filename)
+{
+	if (context) {
+		if (*context) {
+			free((*context)->filename);
+		} else {
+			*context = malloc(sizeof(espeak_ng_ERROR_CONTEXT_));
+		}
+		(*context)->filename = strdup(filename);
+	}
+	return status;
+}
+
 #pragma GCC visibility push(default)
 
+ESPEAK_NG_API void espeak_ng_ClearErrorContext(espeak_ng_ERROR_CONTEXT *context)
+{
+	if (context && *context) {
+		free((*context)->filename);
+		free(*context);
+		*context = NULL;
+	}
+}
+
 ESPEAK_NG_API void espeak_ng_GetStatusCodeMessage(espeak_ng_STATUS status, char *buffer, size_t length)
 {
 	switch (status)

src/libespeak-ng/error.h

+/* Internal error APIs.
+ *
+ * Copyright (C) 2016 Reece H. Dunn
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see: <http://www.gnu.org/licenses/>.
+ */
+#ifndef ESPEAK_NG_ERROR_API
+#define ESPEAK_NG_ERROR_API
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+typedef struct espeak_ng_ERROR_CONTEXT_
+{
+	char *filename;
+} espeak_ng_ERROR_CONTEXT_;
+
+espeak_ng_STATUS
+create_file_error_context(espeak_ng_ERROR_CONTEXT *context,
+                          espeak_ng_STATUS status,
+                          const char *filename);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif