Somebody would just want to defer context creation after parsing
arguments or doing some validations without any particular setup, thus
having to write even the {} is annoying.
Encourages vectorization and generic usage even more. Some functions
were rewritten to make use of the new features, resulting in shorter and
more readable code. This also fixes the annoying naming collision with
WINAPI Rectangle() function.
The old Rectangle is now subclass of Range2D, is marked as deprecated
and will be removed in future release.
Saves unnecessary heap allocation and saves user from the burden of
explicit deletion, otherwise the usage is the same. Polymorphic types
can't be done using `std::optional`, will fix that later.