Encapsulation, CMake,... (Too many changes)

[jgsogo]

Hi,

This is a really big (bad-practice) pull request with lots of changes addressing several issues:

• The most important one is related to encapsulation. Now wnb::wordnet is presented as a class with public functions and private members.
• WordNet data can be downloaded when generating the project with CMake
• Wnb is compiled and used as a library also for tests
• ...

I've also worked in building the graph faster (debug, msvc) but I think it won't be possible without tweaking default (and useful) preprocessor variables (_ITERATOR_DEBUG_LEVEL). I've written about it here (it is in spanish but I think that the photos are self-explained and the video at the end explains the most important thing).

Regards,