* Bump API patch number and header version number to 20 for this
update.
Github Issues:
* Replaced existing reference pages by text automatically extracted
from the specification source, or generated from vk.xml in some
cases. This isn't a complete solution for the reference pages, but
puts them in a much better state. The ref pages (only) are now
placed under a CC BY open source license, which is more current than
the obsolete license previously used.
Further improvements to the pages should not edit them directly, but
instead concentrate on the specification source from which the ref
pages are being extracted (public issues 44, 55, 160; internal issue
389).
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