Added check and define for wide char support

Try to figure out if wide character support is available and provide
the necessary define for toxic.

src/chat.c

@@ -2,6 +2,10 @@
  * Toxic -- Tox Curses Client
  */
 
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
 #include <stdlib.h>
 #include <string.h>
 #include <stdint.h>