Fix PHPUnit fatal errors compatibility with void.

add needed type hints for phpunit8

This will break a lot of plugin tests, but can't be avoided

moved all parsing related namespaces to their own

split out parser modes into their own files

This moves all the parser classes into their own namespace and files.
Next up are the handler classes.

I'm not sure about the namespace, yet. A nested na

split out parser modes into their own files

This moves all the parser classes into their own namespace and files.
Next up are the handler classes.

I'm not sure about the namespace, yet. A nested namepspace Parser\Modes
would probably make more sense... we'll see.

This also removes the duplicated coded in the Plugin mode. We now use
the plugin trait and can inherit from AbstractMode instead.

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increase test coverage for code and file

code - test correct recognition of downloadable filename token
file - test correct recognition of syntax name & downloadable filename tokens

Simple test cases for code and file token fix