* Update release number to 72.
Github Issues:
* Restructure the repository to put the specification `Makefile` and
associated spec source material at the top level, `vk.xml` and
associated scripts material in `xml/`, and generated include and source
files in `include/vulkan/` and `src/ext_loader/`, respectively (public
issue 436).
* Add missing bullet point markup to flink:vkCmdCopyImage valid usage
statement, so it gets a VUID assigned (public issue 627).
* Fix broken links in a couple of extension appendices (public pull
request 665).
* Add the \<platform> tag to the index in section 4.1 of the registry
schema documentation, and add the protect= attribute of \<extension>
tags to the comments in `registry.rnc` (public issues 673, 678).
* Add missing valid usage statements for sparse image interactions to
flink:VkImageCreateInfo (public pull request 675).
* Fix improper usage and grammar of "`can: not`" (public pull request
681).
* Remove duplicate spec language and NOTE on present layout between the
flink:vkAcquireNextImageKHR and flink:vkAcquireNextImage2KHR commands
(public pull request 685).
* Fix some typos and markup issues (public pull request 689; public issues
642, 667, 687).
* Fix typo etext:VK_EXTERNAL_SEMAPHORE_HANDLE_TYPE_FENCE_FD_BIT ->
ename:VK_EXTERNAL_SEMAPHORE_HANDLE_TYPE_SYNC_FD_BIT in the
<<external-semaphore-handle-types-compatibility, External semaphore
handle types compatibility>> table (public pull request 691).
Internal Issues:
* Remove the need for the "`noautovalidity`" attribute on extension
structures in `vk.xml`. It is now implied by the "`structextends`"
attribute instead (internal issue 942).
* Replace uses of "`currently bound`" with "`bound`", since "`currently`"
is redundant and distracting, and add a corresponding rule to the style
guide (internal issue 993).
* Fixed subtle issues with the last updates to flink:vkAcquireNextImageKHR
language that had resulted in ambiguities (internal issue 1178).
* Make it clear that only one query of a given type is allowed at a time
by reordering valid usage statements for flink:vkCmdBeginQuery and
flink:vkCmdEndQuery, and removing redundant ones (internal issue 1213).
* Swapped OL1 and OL3 in `tessparamUL.svg` to match previous version, and
fixed where "`(no edge)`" appears (internal issue 1215).
Other Issues:
* Fixed a minor problem with the valid usage statement extraction script,
and corresponding markup in the spec source.
New Extensions:
* `VK_AMD_shader_core_properties`
* `VK_EXT_descriptor_indexing`
* `VK_NV_shader_subgroup_partitioned`
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