Automatically generate test data

This PR enables the `atoum/praspel-extension` in order to automatically generate test data. In this case/PR, since most of the data can be specified by a regular expression (most of the time, written in the code), tests will handle more realistic test data, and therefore, we will be able to detect more bugs or regressions.

The `atoum/praspel-extension` can be used to generate a wide range of data, from regex to grammar, through date, scalar types, objects, arrays etc. This can be useful I think.
After that line, we have to do a new `composer install`

Why ?

Because to build the phar, we don't want the dev dependencies and also, why not optimizing the autoloader ? :)
After the phar is built, We have to run tests, so we now need dev deps.

But why running tests after the phar is built and not before ?

Tests ran after the phar is built are functional tests. We run them here because they'll test both pickle source version and phar version.