Keep first backup of this day

it holds the version of the blog which was here "today in the morning".

this is useful for those who, like me, first do "bb.sh rebuild" few times
before realizing "oh damn I screwed up everything".

Note: you are not expected to screw up on midnight.

bb.sh

@@ -1022,6 +1022,10 @@ do_main() {
         tar cfz ".backup.tar.gz" *.html &&
         chmod 600 ".backup.tar.gz"
 
+    # Keep first backup of this day containing yesterday's version of the blog
+    [ "$(date -r .yesterday.tar.gz +'%d')" != "$(date +'%d')" ] &&
+        cp .backup.tar.gz .yesterday.tar.gz &> /dev/null
+
     [[ "$1" == "reset" ]] &&
         reset && exit