Added itoa* functions prototypes

Author: cmaglie

api/itoa.h

@@ -0,0 +1,37 @@
+/*
+  Copyright (c) 2016 Arduino LLC.  All right reserved.
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library 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 Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+*/
+
+#pragma once
+
+// Standard C functions required in Arduino API
+// If these functions are not provided by the standard library, the
+// core should supply an implementation of them.
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+extern char* itoa(int value, char *string, int radix);
+extern char* ltoa(long value, char *string, int radix);
+extern char* utoa(unsigned value, char *string, int radix);
+extern char* ultoa(unsigned long value, char *string, int radix);
+
+#ifdef __cplusplus
+} // extern "C"
+#endif
+