D pull request test badge

[Brad Anderson]

I threw together a little tool that outputs an image with 
autotester results.

https://dtestbadge.appspot.com/

You just paste the Markdown:

     ![Test Results](https://dtestbadge.appspot.com)

anywhere on the pull request's page and it'll show an image with 
the pull request's current test results. It uses HTTP referer to 
figure out which pull's tests to look up. Ideally this could be 
moved onto the actual autotester but then Brad would have to fuss 
around with getting SSL working (i.e. HTTP referer doesn't get 
set when transitioning between SSL sites like GitHub to non-SSL 
sites).

The goal is to make easy access to test results inline with the 
pull requests themselves.  The greasemonkey script does this job 
wonderfully and with more information but not everyone uses it. 
This would work for everyone.

I've added one of these badges in a comment to test on this pull 
request if you want to see what it looks like: 
https://github.com/D-Programming-Language/phobos/pull/645#issuecomment-6597823

You can also just do direct links like so: 
https://dtestbadge.appspot.com/phobos/645.png

Regards,
Brad Anderson