uvalue and polymorphic types about meta.hpp

[BlackMATov]

Right now, "uvalue" doesn't support any casts and works like std::any with little specific features. But it can be added because I already do something like this in function calls (when we call functions with reference or pointer attributes on base classes). Of course, it will work only for registered classes with correct "base_<>" attributes.

I'll create a task for this feature!

[innochenti]

thank you. I think it will be useful.

[BlackMATov]

Upcasting is now supported. New example: UValue