prioritize "content" tag over "description"

add module docstring

upgrade to deltabot-cli 6.1.0 (new breaking API)

also improve message deletion and don't send message to bots when
scanning QR

revert to use a file for lastcheck

fix on_start()

fix bug in _check_feed_task()

add --no-time option

update to deltabot-cli v4

update deltabot-cli dep

update deltabot-cli dependency