Add carbon.exceptions
Add carbon.exceptions

For now, this only contains CarbonConfigException, but we can add
more later down the road depending on what types of failure conditions
we want to gracefully handle and report. I see a lot of ceres related
potential here.

JeanFred/carbon,graphite-project/carbon,criteo-forks/carbon,obfuscurity/carbon,deniszh/carbon,mleinart/carbon,lyft/carbon,benburry/carbon,pratX/carbon,obfuscurity/carbon,johnseekins/carbon,xadjmerripen/carbon,cbowman0/carbon,protochron/carbon,criteo-forks/carbon,cbowman0/carbon,piotr1212/carbon,kharandziuk/carbon,graphite-server/carbon,benburry/carbon,xadjmerripen/carbon,krux/carbon,JeanFred/carbon,pu239ppy/carbon,graphite-server/carbon,iain-buclaw-sociomantic/carbon,pratX/carbon,protochron/carbon,deniszh/carbon,iain-buclaw-sociomantic/carbon,kharandziuk/carbon,piotr1212/carbon,pu239ppy/carbon,graphite-project/carbon,johnseekins/carbon,krux/carbon,lyft/carbon,mleinart/carbon