Scaffold files, implement array subject, implement array be size matcher

[BrunoRoemers]

First steps towards implementing array support (#177). This PR is far from complete but this way @ko1nksm can give early feedback.

I suggest we create a new branch to develop this feature until it is ready for the master branch.

Done so far:

• [x] Created the folder structure as suggested
• [x] Implemented array subject
• [x] Implemented be size <n> matcher
• [x] Created examples-array folder (which I'll use to run experiments for the time being)