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.

Review the repository's existing component folders and their include/ directories, then compare them with the proposed include/datasketches layout and the pybind11 precedent linked in the issue. Before changing files, confirm that maintainers have agreed on a target organization; done would require an accepted layout that provides a single include path for foreign build systems.

Written by the indexing model from the issue text.