Ex.:

```
Error unpacking a non unpackable Ast node on `$(binary_xor?... {` at line 29 with context: [
    "^"
]

Hint: use a non ellipsis expansion as in `$(binary_xor ? {`
```

cc ircmaxell/php-compiler#29

```
$ast->{'some deep token'} = new Token(T_STRING, 'patch');
```

Ref: github.com//pull/59

This reverts commit f0d1407.

Closes #19 🎉

From now on, the supported signature for expanders is:

```
function(Optional<Ast|TokenStream> $subject, Optional<Engine> $e) : Ast|TokenStream;
```

Support for nested Ast based expanders through Yay DSL also allowed:

Ex.:

```php
>> {
    $$(my_cheers_ast_expander(
        $$(my_hello_ast_expander(
            $(name_ast_node)
        ))
    ));
}
```

Given:

```php

function my_hello_ast_expander(\Yay\Ast $ast) : \Yay\Ast {
    return new \Yay\Ast($ast->label(), new Token(
        T_CONSTANT_ENCAPSED_STRING, "'Hello, {$ast->token()}. From Ast.'", $ast->token()->line()
    ));
}

function my_cheers_ast_expander(\Yay\Ast $ast) : \Yay\Ast {
    $str = str_replace("'", "", (string) $ast->token());

    return new \Yay\Ast($ast->label(), new Token(
        T_CONSTANT_ENCAPSED_STRING, "'{$str} Cheers!'", $ast->token()->line()
    ));
}

```

Thanks @assertchris for reproducing bugs and pushing tests.

- Augment error messages with their respective line and filename using the
same formating as the PHP engine itself. This allows IDEs to parse both
preprocessor and runtime error message the same way;
- Use a `YayPreprocessorError` instead of stdlib exceptions that can come
from any random user space code;

Using a stream wrapper requires url include enabled and this is
considered too unsafe for most setups. With that in mind I have
no reason to maintain this feature.

Other methods involving composer autoload trickery or xray
(https://github.com/marcioAlmada/xray) extension have been
considered preferable according to community usage history.

YAY!

Usage:
  yay
  yay <file>
  yay --macros=<macros>
  yay --macros=<macros> <file>
  yay -h | --help
  yay --version

Options:
  -h --help         Show this screen.
  --version         Show version.
  --macros=<macros> PHP glob pattern for macros to be loaded. Ex: my/macros/*.yay [default: '']

Examples:

```
# Process file:
yay input.php > output.php

# Process file, preload project macros:
> yay --macros="./project-macros/*.yay" input.php > output.php

# Process stdin:
> cat input.php | yay > output.php

# Process stdin, preload project macros:
> cat input.php | yay --macros="./project-macros/*.yay" > output.php
```

This allows the script to continue if xdebug can't be disabled
(most likely bc it isn't there in the first place)