deps: LevelDB 1.22

[tynes]

This Pull Request bumps the vendored version of LevelDB to 1.22.

I have tested it on both Windows and Linux. It builds and the included test suite passes on both systems.

There are a lot of changed files but the most important one to look at is https://github.com/tynes/bdb/blob/leveldb-1.22/deps/leveldb/leveldb.gyp

Some of the build variables have changed, I think that I removed the dead ones and added the required new ones. I directly copied the leveldb directory from the sources at https://github.com/google/leveldb/releases/tag/1.22

[braydonf]

Any progress with updating upstream leveldown? As there are very few tests for bdb, that will probably be necessary to get more complete testing.