Warn if Consumer is naively configured in a way that will cause busy-looping
Revise message re: code review
Update docs to reflect actual behaviour of MaxWaitTime=0
Use sarama.Logger.Println rather than log.Println
Move config check to matched check for consistency
Phrasing/syntax tweaks.

Also make the warning message point to the documentation.
Merge pull request #42 from Shopify/warn_on_poor_configuration

Warn if Consumer is naively configured in a way that will cause busy-looping