Log Message:
leveldb: updated to 1.22

Release 1.22
Corrected formatting to be compliant with the Google C++ Style Guide.
Specifically export the WriteBatch::Handler inner class for Windows link.
Merge pull request 665 from cheng-chang:coding.
Merge pull request 669 from pavel-pimenov:fix-readme-windows-mkdir.
Merge pull request 472 from zhoudayang:patch-1.
Merge pull request 339 from richcole-at-amazon:master.
Restore soname versioning with CMake build.
Other miscellaneous cleanups, fixes, and improvements.

Release 1.21
Switched to using Copybara for project synchronization.
Minor cleanup in ports.
Silence unused argument warnings in MSVC.
Add tests for empty keys and values.
Switch corruption_test to use InMemEnv.
Replace AtomicPointer with std::atomic.
Make InMemoryEnv more consistent with filesystem based Env's.
Align windows_logger with posix_logger.
Improve CI configuration and added AppVeyor (Windows CI) badge to README.
Added native support for Windows.
Make WriteBatch::ApproximateSize() const.
Fix PosixWritableFile::Sync() on Apple systems.
Fix fdatasync() feature detection in opensource build.
C++11 cleanup for util/mutexlock.h.
Rework threading in env_posix.cc.
Remove InitOnce from the port API.
Expose WriteBatch::Append().
Fix documentation for log file growth.
Add move constructor to Status.
Replace port_posix with port_stdcxx.
Reimplement ConsumeDecimalNumber.
Document the building process.
Replace NULL with nullptr in C++ files.
Remove PLATFORM_IS_LITTLE_ENDIAN from port/posix.h.
Add more thread safety annotations.
Require C++11.
Replace SIZE_MAX with std::numeric_limits.
Add CMake build support.
Enable thread safety annotations.
leveldb::DestroyDB will now delete empty directories.
Replace SSE-optimized CRC32C in POSIX port with external library.
Fix file writing bug in CL 170738066.
Fix use of uninitialized value in LRUHandle.
Fix issue 474: a race between the f*_unlocked() STDIO calls in env_posix.cc and \ 
concurrent application calls to fflush(NULL).
Use __APPLE__ instead of OS_MACOS. The former is compiler-provided.
Report missing CURRENT manifest file as database corruption.
LevelDB: Add WriteBatch::ApproximateSize().
Other minor fixes, code cleanup, and documentation improvements.