Switching from Makefile to CMake

[yangyushi]

I hand-coded all the makefiles which may not be a good demonstration... At some point I will shift this to CMake

[yangyushi]

Experimenting around my other projects, I find some ideas.

• add Eigen and pybind11 as submodules.
• just include the source code of voro++ with correct building configurations

The final goal should be that the user will need to use CMake to compile all C++ code, and to use pip to install all Python packages.

[yangyushi]

The commits 463a8b1 and 10b180c removed the dependency on the pybind11, Eigen, and voro++.

The user will still have to use build.sh to build the package, but it should be easier now. I will work towards the goal, of using CMake for building the package.