(doc) Document the new error system.
(doc) Document the new error system.

reem/iron,leeric92/iron,fenhl/iron,lavriv92/iron,Undeterminant/iron,steveklabnik/iron,charsyam/iron,bvssvni/iron,armed/iron,lcqiang521/iron,shaunstanislaus/iron,mneumann/iron,green-panther/iron,ilkosta/iron,youprofit/iron,albperezbermejo/iron,ahwatts/iron,jlegendary/iron,markgeek/iron,iron/iron,mzaccari/iron,dryganets/iron,dorfsmay/iron,badboy/iron,beni55/iron,Jeff-xchn/iron,shama/iron,tempbottle/iron