Review all print statements

[wleoncio]

Just a reminder before we send the package to CRAN: it's not advisable that package functions print things that the user cannot suppress somehow. All print statements should be either:

1. Converted to message(), warning() or error() depending on the case;
2. Converted to cat() or sprintf() and conditioned tomy_print or other verbose-like argument for cleaner printing of intermediate results

This is something CRAN reviewers invariably ask us to change, so we would save at least one review round (not to mention improve user experience) by fixing it beforehand.

[Theo-qua]

Okay, could we convert print for fold to a message because I will like that to be printed.