add a score endpoint by rule

@BenDoyle 

This is mostly  a check that we can add endpoints after the fact -- and it works! 

It also implements the useful score rule that has some flaws:
 - It doesn't memoize like it should so it just counts all pr's merged every time
 - It's counting all closed pr's and making a request for each to see if it's been merged we might get rate lmited
 - it doesn't care about actually composer of committers so people could game the system by pushing others changes and creating PR's

The good news is we can now add the rest of the code via rules, and have just one bootstrapping rule.