Updates for PHP8 & GPL, a few IndieWeb TLDs, new functions

overall:

• license CC BY-SA 4.0 (for GPL compat)
• PHP 8 compat
• various other bug fixes, better handling of function params

new file:

• cassis-lab.php — functions that would work well as CASSIS but have no known client-side use-cases

new functions:

• ctype_lower
• stripos
• prepath_of_uri
• segment_of_uri
• fragment_of_uri
• get_absolute_uri
• is_html_type
• xpr_attr_starts_with_has_class
• get_auto_linked_urls

improved functions:

• auto_link_re — new TLDs for IndieWeb sites
• auto_link — link @-domain (e.g. rather than just Twitter handle)