Refactor to improve file organization

[yungyuc]

The refactor includes:

• Collect cpp and hpp files to a single directory.
• Separate files of binary and shared object from the library code.
• Separate the CMakeLists.txt file list variables in the directory hierarchy.
• Separate wrapper building functions to distinct files for parallel build.
• Create modmesh/buffer.hpp.
• Fix error return of setup.py, which didn't return an error code when the sub processes fail. Fix by throwing an exception.