Optimized/Rebuild `LevelDB` Native for `LevelDBStore`

[cschuchardt88]

Change Log

• Optimized LevelDBStore
• Code Cleanup
• Rebuild

[cschuchardt88]

@cschuchardt88 @Jim8y @vncoelho @superboyiii @chenzhitong @AnnaShaleva Review Please

[cschuchardt88]

@vncoelho This is refactoring everything. Im sure there is performance benefits. But that isn't the point of this PR. This PR fixes dotnet management of the leveldb objects from marshal objects. Also you have access to leveldb classes for easy accessibly.

Example

var options = new Options { CreateIfMissing = true };
using (var db = new DB(options, path))
{
    db.Put("NA", "Na");

    using(var batch = new WriteBatch())
    {
        batch.Delete("NA")
             .Put("Tampa", "Green")
             .Put("London", "red")
             .Put("New York", "blue");
        db.Write(batch);
    }
}

[cschuchardt88]

@shargon @Jim8y review please

[cschuchardt88]

@AnnaShaleva

Also, have you tested the resulting code against the current mainnet/testnet? Is the state compatible?

Yes

This adds the full features of the leveldb library.

[shargon]

Repository moved to neo, please re-open there