Add no purge, manual delete options (#12)

- Add htmx, hx attributes
- Only add/update items since last check
- Move messages to session to persist across redirects
- Polish styles a bit (still WIP)

src/user-config.dist.php

@@ -28,6 +28,7 @@ const DATE_TIME_FORMAT = 'F j, Y \a\t g:ia';
 
 /**
  * How should item purging be done? (Purging never applies to bookmarked items.) Options are:
+ * - Feed::PURGE_NONE - Do not purge items
  * - Feed::PURGE_READ - Purge all read items whenever purging is run (will not purge unread items)
  * - Feed::PURGE_BY_DAYS - Purge read and unread items older than a number of days (PURGE_NUMBER below)
  * - Feed::PURGE_BY_COUNT - Purge read and unread items beyond the number to keep (PURGE_NUMBER below)