Provides a 12.6% size savings for vkspec.html
(697770 B -> 609679 B, gzipped), because:
(1) plaintext is smaller than base64-encoded plaintext, and
(2) base64 does not gzip as well as plaintext SVG.
associated material at the top level, vk.xml and associated material in
xml/, and generated include and source files in include/vulkan/ and
src/ext_loader/, respectively (public issue 436).
Kai Ninomiya
Jon Leech