add utf8_char_t struct

src/append_buffer.c

@@ -2,8 +2,8 @@
 
 extern struct editorConfig E;
 
-void abAppend(struct abuf *ab, const char *s, int len) {
-  char *new = realloc(ab->b, ab->len + len);
+void abAppend(struct abuf *ab, const unsigned char *s, int len) {
+  unsigned char *new = realloc(ab->b, ab->len + len);
 
   if (new == NULL) {
     return;