Output Intents, shading patterns, strikethrough text and many more

Added

• support for Output Intents on document level - thanks to @lka
• support for shading patterns (gradients) - thanks to @andersonhc - PR #1334
• support for setting a minimal row height in tables
• support for v_align at the row level in tables
• new optional reset_page_indices parameter for insert_toc_placeholder()
• support for strikethrough text
• support for first_line_indent in text_region.Paragraph
• new ViewerPreferences.print_scaling
• documentation on fpdf2 internals
• documentation on generating Aztec Codes
• added Slovenian translation of the tutorial: Vodič - thanks to @DeepBlackHole
• support for adding TrueType fonts that are missing the .notdef glyph - issue #1161 - thanks to @spacegaori
• improved SVG image parsing speed by 50% to 70% - thanks to @petri-lipponen-movesense - PR #1350
• added tutorial "tuto7" (in English and German) with documentation to create PDF/A files with fpdf2 - thanks to @lka

Fixed

• FPDF.write_html(): Fixed rendering of content following <a> tags; now correctly resets emphasis style post </a> tag: hyperlink styling contained within the tag authority. - issue #1311
• FPDF.footer() does not "leak" its text style to the table of contents anymore
• FPDF.table(): Fixed heading styles containing underline failing to render.
• FPDF.ln(): the method now allows a value of 0 to be provided for h.
• font optimization: only include fonts effectively used in the final PDF document. Fonts added via set_font() or add_page() but not actually used in the document are no longer included in the final output. This reduces file size and improves performance, especially for documents with many fallback fonts. - issue #1382
• a KeyError was raised in some specific cases when auto-downscaling images - issue #1409

Changed

• heading rows of tables are never rendered "alone" on a page anymore