Update the year in copyright

[y-martinez]

• There are many files with the copyright notice outdated, that is, finishing the last year. Maybe these should be updated to 2021
• Also, I found that in some files there is the old URL of the project hosted in http://code.google.com/p/cdpedia/ I think that this should be updated with the URL of the project hosted in https://github.com/PyAr/CDPedia

These are simple changes but not for that less important, now more than the version 0.9 is out.

If this issue is accepted I would like to work on it. @facundobatista @fzuccolo