GitLab

Adding a switch for the API type in the script, much of the content can
be re-used between Vulkan and OpenXR.

Updated the README for the new OpenXR header.

better usage instructions for value serialization, and now reflects the
C/C++ split.

The ability to convert a VkResult to a readable string is too useful to
keep locked away just inside the std::error_code.

As such, that functionality has been shifted to a separate header that
provides just the vkResultToString(VkResult) function standalone, and
now also be C-compatible.

In the original version of this library the different mini libraries,
including for serialization had a separate file for each Vulkan header
version.

This new library set seeks to fully consolidate these into single files,
instead properly segmenting the files using version macros if the types
cannot be made fully forward/backward compatible.