Merge pull request #61 from pbechu/barcode-validator

Barcode validator
Mention the new barcode validator
Add Pierre-Baptiste to the contrib list
Replace unary + operator in favor of its binary version

Here's a nice explanation for future reference:
https://stackoverflow.com/questions/16624131/what-do-def-and-def-mean
Remove extra chars from the require's
Introduce ActiveValidators.activate for 3.0.0
Release 3.0.0
Release 3.0.1

This release stops require all the validators by default