all-contributors bot

[daxpryce]

First off, sorry for spamming the crap out of everyone while I tried to get this set up. I had to do a number of things to make it work:

1. The CI build ignores any changes to .all-contributorsrc and CONTRIBUTORS.md. This means a project admin will have to merge any changes the bot gives us - but we have to do that anyway because the bot can't agree to the Microsoft CLA. I'm trying to figure out if we can fix that part, but in the meantime...
2. It does not work well if you try to add someone and then add a new someone in a different PR. You may have to periodically resolve conflicts manually. Maybe it would work better if we turned alphabetization off, but it isn't for now... and so that's that.
3. Again, sorry for all the spam. I tried to handle everything via PRs and the github bot but trying to do that while adding everyone who ever contributed was going to turn into a conflict resolution nightmare and I just had no interest in that.

On the upside, it's done now. Also, we can and should add people like Jovo and Jonathan Larson and other mentorship types; take a look at all the different roles someone can be added for at this link