Merge remote-tracking branch 'remotes/armbru/tags/pull-qapi-2020-09-08' into staging

QAPI patches patches for 2020-09-08

# gpg: Signature made Tue 08 Sep 2020 07:06:52 BST
# gpg:                using RSA key 354BC8B3D7EB2A6B68674E5F3870B400EB918653
# gpg:                issuer "armbru@redhat.com"
# gpg: Good signature from "Markus Armbruster <armbru@redhat.com>" [full]
# gpg:                 aka "Markus Armbruster <armbru@pond.sub.org>" [full]
# Primary key fingerprint: 354B C8B3 D7EB 2A6B 6867  4E5F 3870 B400 EB91 8653

* remotes/armbru/tags/pull-qapi-2020-09-08:
  qapi/block-core.json: Fix nbd-server-start docs
  qapi: Fix indentation, again
  qapi/migration.json: Fix indentation
  qapi: Make section headings start a new doc comment block
  qapi: Reject section markup in definition documentation

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>