meta: header for misc metaprogramming tools that lives in `blue_sky::meta`
meta: header for misc metaprogramming tools that lives in `blue_sky::meta`

First commit contains `forward_as<T, AsT>` that is imilar to
`std::forward` but if passed value was of type `AsT` with all props
copied from source type `T`.

uentity/blue-sky-re,uentity/blue-sky-re,uentity/blue-sky-re