Adding two options required for compatibility with 3rd party components

I added two new options.

These options are implemented only in [`\Masterminds\HTML5\Parser\DOMTreeBuilder`](https://github.com/PHPPowertools/html5-php/blob/master/src/HTML5/Parser/DOMTreeBuilder.php) and have the following purpose :

* `implicitHtmlNamespace` = Allows the use of createElement instead of
createElementNS for HTML elements. This is required for compatibility
with [`\PHPPowertools\DOM-Query`](https://github.com/PHPPowertools/DOM-Query) and for compatibility with [`\Symfony\Component\CssSelector\CssSelector`](https://github.com/symfony/CssSelector).

* `target` = allows an existing DOMDocument (or subclass thereof) to be
passsed to the DOMTreeBuilder instead of creating a new one. This
option is required for compatibility with [`\PHPPowertools\DOM-Query`](https://github.com/PHPPowertools/DOM-Query)