Clarify which symbols are part of public API and which are implementation details

[Hawk777]

The README explains in general how to use Vulkan-HPP, but it doesn’t really go into details. So, to figure out e.g. individual function signatures, I’ve taken to just browsing the header file. Unfortunately, the header file has very few comments, so I’m not sure which things I discover I’m really allowed to use—which are parts of Vulkan-HPP’s public API, and which are implementation details which are only in the header file for technical reasons (i.e. because Vulkan-HPP is a header-only library so everything is in header files)?

For example, if I have a Result lying around, am I allowed to call throwResultException myself, or is that an implementation detail which might get renamed or deleted in a future version of Vulkan without warning?

It would be good if implementation details were either commented as such, or perhaps put into an impl namespace or something like that.

[Pacheco95]

Meybe put implementation details in a different namespace, e.g. priv