Better parser error reporting

```
int test() {
return 1;
}
int main(void) {
if (!test()) return -3;
return 0; }
```
Produces ` Excessive output after the end of a translation unit at line 5, column 10: KeywordInt int.`

If I comment out `if (!test()) return -3;` then things starts working.

Okay, I figure out while I wrote this, we lack of support for `!` operator for conditions, but I think we should do something about better user reporting.