Merge pull request #1 from singingwolfboy/master

Minor improvements
Merge pull request #2 from singingwolfboy/master

Added report script to get median durations
Don't pretend that issues are pull requests

The old code was iterating issues, and if there was no pull request
link, it would create dummy data for the pull request information.  But
this script is meant to only look at pull requests, so we don't need to
do that, right?
Merge pull request #3 from nedbat/ned/only-pull-requests

Don't pretend that issues are pull requests