`std::make_unique<T[]>(size)` always zero-initalizes the array.
C++20 has `std::make_unique_for_overwrite` to avoid that, while
older C++ versions can use the approach applied here.
- Add file documentation to about 1/4 of the files in Source
- Copy over a lot of the documentation from the sanctuary/notes repo
- Standardise all the existing documentation
- Create a configuration for Doxygen
- Add more documentation (engine.cpp is now fully documented)
Now diablo.h is treated in the same way as all other header files of
Source, as it only contains the declarations of global variables and
functions of diablo.cpp.
Besides consistency, this also enables mods to include diablo.h just
like any other header file without having to include every header file
(and without having to include C++ specific aspects of the now all.h).