Nuspell version 5.1.3

Added

• Added Vcpkg manifest file called vcpkg.json for easier development and
  testing, mainly on Windows.

Changed

• The build-only and test-only dependency Catch2 is now pulled with
  FetchContent if first it is not found with find_package. The Git submodule
  is no longer used.

Fixed

• The documentation generated by Doxygen no longer shows the inline namespace
  used for versioning of the ABI. It was not of interest to users of the
  library.