Html5validator

Incorporate https://github.com/svenkreiss/html5validator/pull/59

* update vnu jar to 18.11.5
* better output check [PR57](https://github.com/svenkreiss/html5validator/pull/57) by [Cyb3r-Jak3](https://github.com/Cyb3r-Jak3)

* update vnu jar to 18.3.0
* pass remaining command line options to ``vnu.jar``
* allow to match multiple file patterns, e.g. ``--match *.html *.css``

* update vnu jar to 17.11.1
* support explicit list of files: ``html5validator file1.html file2.html``
* new command line options: ``--no-langdetect``, ``--format``
* new tests for ``--show-warnings`` flag
* refactored internal API
* bugfix: check existence of Java
* bugfix: split Java and vnu.jar command line options

* update vnu jar to 17.9.0
* suppress a warning from the JDK about picked up environment variables

* update to vnu.jar 17.3.0
* lint Python code