Address Robert's feedback

@@ -43,11 +43,11 @@
 size_t str_length(const str_t *);
 boolean_t str_copy(const str_t *, str_t *);
 void str_set(str_t *, const char *, size_t);
 boolean_t str_append(str_t *, const char *, size_t);
 boolean_t str_append_str(str_t *, const str_t *);
-boolean_t str_append_c(str_t *, int);
+boolean_t str_append_c(str_t *, char);
 boolean_t str_insert(str_t *, size_t, const char *, size_t);
 boolean_t str_insert_str(str_t *, size_t, const str_t *);
 boolean_t str_erase(str_t *, size_t, size_t);
 
 str_pair_t *str_pair_init(str_pair_t *, sysdem_ops_t *);