added screen_duplicated method in rss.py
add a reminder to modify task.py
added a reminder to read etag/modified
added code to return etag, modified every time the server is quried.
updated add_entries boundary checkers
changed add_entries to update
renamed screen_duplicated to screen_duplicates, and added some docs
moved screen method back to database; renamed screen to value-add-process
wrote dedup to return non-existing entries
imported database
prepared to write _value_added_process
cleaned database.update
added a void update_feed