Unit test resources organization

[remikey]

As pointed out by @pictavien in #80, the project could benefit in a better organization of unit test resources.

This issue aims at globally defining the plan of how resources should be organized, document it, and actually apply it.

[remikey]

Remark worth noting:

• Having result resource files in the same directory as the input ones has proven to be cumbersome when updating copyright notices with Intellij IDEA.

  When using Update copyrights in IDEA, it will also add copyright notices in any file it considers lacking one. It is the case of result files used when testing the Serializers. However, adding a copyright notice in a generated file will break the tests.
  Having input files and output files in separate directories would easy discriminating between what should actually be commited and what should not.
  It would also probably be useful when testing / generating test files during development.