Add a mode to check if we're above 1000 search results for `parent` and `all`

[justinharringa]

#169 highlights an issue with GitHub search where we can't get more than 1000 search results for the all and parent commands. It would be nice to have a mode where a user could run DFIU and get a zero exit status if we're below 1000 and a non-zero exit status and message that we're at or above 1000.

all credit for this idea goes to @npwolf