Reverts the php-ast AST back into (somewhat) PSR-compliant code
This release drops support for versions 10 and 20 of php-ast, whilst adding support for versions 30, 35, and 40.
Support for PHP 7.2 has also been added, with backwards compatibility with PHP 7.0 and 7.1 maintained.
The dependency on ext/tokenizer has also been removed in favour of using the now-provided flags from the php-ast extension.