twitter-backup: merge store_tweets and store_tweets_to

Also display the JSON filename.
twitter-backup: drop custom min(), max()
twitter-backup: add get_filename()
twitter-backup: clean up some things
twitter-backup: only increment $page if fetch succeeded
goto-vim: also try to -e first line in a multiline selection
sprunge: handle '-' as stdin specially
sprunge: sprunge the primary selection if on X11 and no files