Ft conclude javadocs

Hi everyone,

today was chosen for work on the documentation of Groundhog. 

I did document almost all modules and classes in the project using Javadocs notation. I just did not document the `br.ufpe.cin.groundhog.http` module, because I understand very little of what it does. But the good news is that it is already partially documented.

Also, I can more clearly understand the code now that I took a full afternoon to browse and document the code. This experience was amazing I wish I could've done it earlier. In my opinion, the source code is not so big but nevertheless is easy to understand how its underpinnings work.

I've also edited and renamed the [Overview](the https://github.com/spgroup/groundhog/wiki/Overview) Wiki page and that also helped me better understand how Groundhog works.

Please review this Pull Request and let me know if there's anything wrong with it or anything else that might prevent its merge with the `master` branch.

Thanks,

-- rodrigo