Add new feed URL, adding /feed to category, tag, type, search, author. Eg. /category/htmly/feed

Far more easier to remember

It's easier to understand more optimal for managing static pages.

See  #564

Add SECURITY.md also fix unexpected behavior with tags in number. See #614

Add last modified time variable (eg. $p->lastMod). Add fallback just in case the tags count not the same.

Publish a post with future date or time, it will go into scheduled posts.

Remove deprecated warning for PHP 8.x

replacing text with new added key values from language files (;errors - Invalid_Error)

This reverts commit 9d25d5e49d.

Allow to use tag like C++ and double check for the same tag slug.

PHP 8 compatibility