Replaces prints with logging functions

[jcemelanda]

This pullrequest replaces the print calls throughout the code with the logging module.

I believe this review could be done by anyone with deep enough understanding of the code to know if the logging methods called are really the best suited ones for each place.

I tried to define the log level of each call based on the code around each print call. Usually I used logging.info, errors when dealing with errors and exceptions and warnings when I saw the message was a warning message.

Fixes #25

[lipemorais]

Great job @jcemelanda !

[jcemelanda]

Thanks! I'll go for it A.S.A.P.

[anaschwendler]

Closed by #163