HTMLdoc v1.8.0

This release fixes a number of issues and removes support for PHP 7.4:

• Fixed issues handling empty attributes in tag::minify(), where the code expected the attribute value to be a string, but if only the attribute name appears, its value would be null
• Improved logic in tag::minify()
• Fixed bug in selector::parse() where when it hit a bracketclose it didn't exit the loop, causing it to parse too much
• Improved tag::find() by making it do work out of a loop
• Added test to findHtmldocTest.php to check it can find items where :not(:pseudo-selector)
• Updated type hints to correct types where #[\ReturnTypeWillChange] as the software now only supports PHP 8.0+
• Added type hints where mixed is required
• Added union type hints on arguments and return types where missing
• Added ability to handle sibling selectors to tag::find()
• Updated htmldoc::collection() to only store unique tags, as sibling find() operations can produce the same node multiple times
• Updated composer dependencies