Color coded errors/warnings/messages/printed text

[czeildi]

By default errors, warnings and messages are all printed red in R which can be confusing as red usually means something wrong but a message can be just informative. I think it would be nice to provide an easy way to create colored messages, like by default red for error, yellow for warning, blue for friendly information etc. With the crayon package this should not be too difficult.

I am thinking about a way that maybe the end-user should be able to control this, or the creator of the package. We could distinguish style further based on the class of the condition.