Centralized Logging

[otaviof]

The command-line needs to print out information and errors for all sub-commands and we would benefit to have a single component responsible for this task. Right now we have a mixture of log and fmt.Printf going on, so we should come up with a new component which will be employed by all others that need to interact with the user.

Please share here your thoughts, and your ideas of what a logging component like this would have to have.