Lmdb

* Add Python 3.11 support.

* Add aarch64 architecture builds. Contributed by odidev.

* Add Python 3.10 support.

* Fix crash relating to caching of transactions. The 'max_spare_txns'
parameter to Environment/open is currently ignored.

* Resolve CI bug where non-Linux wheels were not being published to PyPI.

* Update bundled LMDB to 0.9.29.

* Add non-bundled testing to CI.

* Remove wheel generation for 2.7 because the manylinux images no longer
support it.

* Allow passing None as a value to transaction.del in CFFI implementation
for parity with cpython implementation.

* Fix Cursor.put behavior on a dupsort DB with append=True.

* Add warning to docs about use of Environment.set_mapsize. This is currently
an unresolved issue with upstream LMDB.

* CFFI implementation: fix a seg fault when open_db returns map full.

* CFFI implementation: fix a bug in open_db in a read-only environment.

* Dowgrade underlying LMDB to 0.9.26. 0.9.27 has a minor defect that will
need to get resolved.

* Migrate CI pipeline from Travis and AppVeyor to Github Actions. Now
includes comprehensive testing across 4 dimensions (OS, Python version,
cpython/CFFI, pure/with mods). Also includes publishing to PyPI.

* Prevent invalid flag combinations when creating a database.

* Add a Cursor.getmulti method with optional buffer support. Contributed by
Will Thompson <willsthompsongmail.com>.

* Upgrade underlying LMDB to 0.9.27.