Add Result function to query Build Results endpoint

This PR adds support for the [Build Result Platform API endpoint][1].


[1]: https://devcenter.heroku.com/articles/platform-api-reference#build-result
It's mainly that it's unrelated. We should deprecate the naaman/hbuild thing, or actually move the repo. Also, I'm tempted to get rid of the whole hbuild dependency altogether and just put it in the endosome/heroku package. It's causing more pain at this point than was originally solving.