Polish and long tail.

• #2750541 diphthong transliteration (release-note callout: changes generated paths)
• #2926312 extensionless filename tokens
• #2844420 permissions when destination exists (rework post-3419618)
• #3476482 multi-part extensions (.pdf.p7m)
• #3099935 leading-letters sharding token
• #2631464 path preview on settings form
• #3167757 stop HTML-escaping token values (BC, needs the minor bump)
• #3182718 taxonomy hierarchy as folder structure (live community patch, igoragatti)