Reorganization proposal

Hi there,

We are consider using datasketches in our C++ environment. The current organization, where there a bunch of folders, each with an `include/` directory, is a bit awkward for integrating into a foreign build system. Projects like [pybind11](https://github.com/pybind/pybind11/) put all of the headers in a single `include/` directory (perhaps with subdirectories underneath). Then there is just a single path to add as an include path.

Would you be open to a reorganization that moved around files to look a bit like this:
```
include/datasketches
count/
count_min.hpp
count_min_impl.hpp
common/
MurmurHash3.h
...
```

Thanks for your consideration.

Esamina le cartelle dei componenti esistenti del repository e le relative directory include/, quindi confrontale con il layout proposto di include/datasketches e con il precedente di pybind11 collegato nella issue. Prima di modificare i file, conferma che i maintainer abbiano concordato un’organizzazione di destinazione; il lavoro sarebbe completato quando esistesse un layout accettato che fornisca un unico percorso include ai sistemi di build esterni.

Scritto dal modello di indicizzazione a partire dal testo della issue.