Plerd-1.900

Changes for version 1.900 - 2026-06-19

Incremental publishing: plerdwatcher now republishes incrementally on a source change, falling back to a full rebuild only when a change can affect shared pages (recent/archive/tag pages and feeds). Scales far better as a blog's archive grows.
All generated files are now written atomically (rendered to a temp file, then renamed into place), so a web server never serves a half-written or empty file, and a failed render leaves the previous file intact.
Promoting webmention sending from experimental to supported feature.
Removing experimental support for storing webmentions.
HTML is now stripped from JSON Feed titles.
Fixing a bug that would sometimes list a post twice on a tag page.
The default post template now shows a "Previous post" link in list view when older posts exist.
Trailing whitespace is now stripped from metadata values.
Assorted correctness and robustness fixes (with added tests), and hardened index.html symlink creation.
Declaring Digest::MD5 and JSON as dependencies.
Requiring DateTime 1.54 or later; older versions could round-trip a post's W3C "time" value into an unparseable form. Thanks to Olivier Auverlot for the report.
Continuous integration moved from the defunct Travis CI to GitHub Actions (Perl 5.32 / 5.36 / 5.40).