Updated D/C++ template comparisons up to C++20.

The comparisons were pre-C++11, and since C++ has developed greatly since then this was due for an update.

To avoid having a crowded table listing every standard or only listing the latest-and-greatest, I opted to just have a single C++ column that calls out differences when present.

I also made the indentation consistent since I was having trouble figuring out where sections began/ended.

Author: Victarus