phoneme: add a phoneme_add_feature internal API method.

Makefile.am

 	src/libespeak-ng/intonation.c \
 	src/libespeak-ng/numbers.c \
 	src/libespeak-ng/readclause.c \
+	src/libespeak-ng/phoneme.c \
 	src/libespeak-ng/phonemelist.c \
 	src/libespeak-ng/setlengths.c \
 	src/libespeak-ng/spect.c \

src/include/espeak-ng/espeak_ng.h

 	ENS_GROUP_ERRNO              = 0x00000000, /* Values 0-255 map to errno error codes. */
 	ENS_GROUP_ESPEAK_NG          = 0x10000000, /* eSpeak NG error codes. */
 
+	/* eSpeak NG 1.49.0 */
 	ENS_OK                       = 0,
 	ENS_COMPILE_ERROR            = 0x100001FF,
 	ENS_VERSION_MISMATCH         = 0x100002FF,
 	ENS_NO_SPECT_FRAMES          = 0x10000CFF,
 	ENS_EMPTY_PHONEME_MANIFEST   = 0x10000DFF,
 	ENS_SPEECH_STOPPED           = 0x10000EFF,
+
+	/* eSpeak NG 1.49.2 */
+	ENS_UNKNOWN_PHONEME_FEATURE  = 0x10000FFF,
 } espeak_ng_STATUS;
 
 typedef enum {

src/libespeak-ng/compiledata.c

 			continue;
 		}
 
+		if (phoneme_add_feature(phoneme_out, item_string, NULL) == ENS_OK)
+			continue;
+
 		switch (item_type)
 		{
 		case tPHONEME_TYPE:

src/libespeak-ng/error.c

 	case ENS_EMPTY_PHONEME_MANIFEST:
 		strncpy0(buffer, "The phoneme manifest file does not contain any phonemes", length);
 		break;
+	case ENS_UNKNOWN_PHONEME_FEATURE:
+		strncpy0(buffer, "The phoneme feature is not recognised", length);
+		break;
 	default:
 		if ((status & ENS_GROUP_MASK) == ENS_GROUP_ERRNO)
 			strerror_r(status, buffer, length);

src/libespeak-ng/phoneme.c

+/*
+ * 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/>.
+ */
+
+#include "config.h"
+
+#include <errno.h>
+
+#include <espeak-ng/espeak_ng.h>
+#include <espeak-ng/speak_lib.h>
+
+#include "phoneme.h"
+#include "speech.h"
+#include "error.h"
+
+enum feature_t {
+	inv, // invalid phoneme feature name
+};
+
+static MNEM_TAB features[] = {
+	{ NULL,  inv },
+};
+
+espeak_ng_STATUS
+phoneme_add_feature(PHONEME_TAB *phoneme,
+                    const char *feature,
+                    espeak_ng_ERROR_CONTEXT *context)
+{
+	if (!phoneme || !feature) return -EINVAL;
+
+	switch (LookupMnem(features, feature))
+	{
+	default:
+		return ENS_UNKNOWN_PHONEME_FEATURE;
+	}
+	return ENS_OK;
+}

src/libespeak-ng/phoneme.h

 	unsigned char length_mod;    // a length_mod group number, used to access length_mod_tab
 } PHONEME_TAB;
 
+espeak_ng_STATUS
+phoneme_add_feature(PHONEME_TAB *phoneme,
+                    const char *feature,
+                    espeak_ng_ERROR_CONTEXT *context);
+
 // Several phoneme tables may be loaded into memory. phoneme_tab points to
 // one for the current voice
 extern int n_phoneme_tab;