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.

检查 repository 现有的组件文件夹及其 include/ 目录，然后将它们与提议的 include/datasketches 布局以及 issue 中链接的 pybind11 先例进行比较。在更改文件之前，确认 maintainer 已就目标组织方式达成一致；只有存在一个能为外部构建系统提供单一 include 路径的已接受布局，才算完成。

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