mdbx: release v0.11.1

Backward compatibility break:
-----------------------------

The database format signature has been changed to prevent
forward-interoperability with an previous releases, which may lead to a
[false positive diagnosis of database corruption](https://github.com/erthink/libmdbx/issues/238)
due to flaws of an old library versions.

This change is mostly invisible:

 - previously versions are unable to read/write a new DBs;
 - but the new release is able to handle an old DBs and will silently upgrade ones.

Acknowledgements:
-----------------
 - [Alex Sharov](https://github.com/AskAlexSharov) for reporting and testing.

Signed-off-by: Leonid Yuriev <leo@yuriev.ru>

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