Move advance() from fe-common/core to core.

src/core/utf8.c

@@ -26,3 +26,18 @@
 #include "module.h"
 #include "wcwidth.c"
 
+int advance(char const **str, gboolean utf8)
+{
+	if (utf8) {
+		gunichar c;
+
+		c = g_utf8_get_char(*str);
+		*str = g_utf8_next_char(*str);
+
+		return unichar_isprint(c) ? mk_wcwidth(c) : 1;
+	} else {
+		*str += 1;
+
+		return 1;
+	}
+}