Add tokenlist, a linked list of lexer tokens

The linked list is doubly linked so the parser can look forward into it
and error reporting can look backward.

This commmit also reworks main to use the tokenlist instead of dealing
with the lexer manually.

src/main.c

@@ -1,5 +1,6 @@
 #include "error.h"
 #include "lexer.h"
+#include "tokenlist.h"
 
 #include <limits.h>
 #include <stdio.h>
@@ -39,24 +40,33 @@ int main(int argc, char *argv[]) {
         print_fn = print_value;
     }
 
-    lexer_t lex = {0};
-    lexer_token_t token;
-    error_t *err = lexer_open(&lex, filename);
-    if (err) {
-        puts(err->message);
-        error_free(err);
-        return 1;
-    }
+    lexer_t *lex = &(lexer_t){};
+    error_t *err = lexer_open(lex, filename);
+    if (err)
+        goto cleanup_error;
 
-    bool keep_going = true;
-    while (keep_going && (err = lexer_next(&lex, &token)) == nullptr) {
-        keep_going = print_fn(&token);
-        free(token.value);
-    }
+    tokenlist_t *list;
+    err = tokenlist_alloc(&list);
+    if (err)
+        goto cleanup_lexer;
 
-    if (err && err != err_eof) {
-        puts(err->message);
+    err = tokenlist_fill(list, lex);
+    if (err)
+        goto cleanup_tokens;
+
+    for (auto entry = list->head; entry; entry = entry->next) {
+        print_fn(&entry->token);
     }
+    tokenlist_free(list);
     error_free(err);
     return 0;
+
+cleanup_tokens:
+    tokenlist_free(list);
+cleanup_lexer:
+    lexer_close(lex);
+cleanup_error:
+    puts(err->message);
+    error_free(err);
+    return 1;
 }