Improve error messages

For example:

```
(foo "blah")
```

Yields this error:

> Lisphp_InvalidApplicationException: nil cannot be applied; see Lisphp_Applicable interface: (foo 'blah') in /Users/igor/lisphp/vendor/lisphp/lisphp/src/Lisphp/List.php on line 18

It's not really user friendly.
