Common structure of base libraries

Right now mapbox-base is a set of small submodules. That makes hard to support consistency between each small repo. Maybe we should place all these files in one repo? Like a std library.

As example, in VisionSDK we want to use optional and variant from mapbox-base and have a troubles:

• optional class is placed inside std::experimental namespace, but variant places in mapbox::util one.
• optional package have different structure from variant. variant have include/mapbox folder that allow me to add include folder to include_directories and use #include "mapbox/variant.hpp". But i can't do the same with optional. Because optional.hpp placed directly inside optional submodule directory

Iniziate esaminando i sottomoduli mapbox-base e confrontando le strutture dei pacchetti e gli spazi dei nomi di optional e variant, in particolare i relativi percorsi di inclusione. Definite una struttura comune del repository e convenzioni coerenti per le inclusioni pubbliche e gli spazi dei nomi, quindi confermate che i casi d’uso di VisionSDK possano utilizzare entrambe le librerie in modo coerente.