Async version of MongoDB.

You should only have one instance of MongoClient in a JVM.

Example:

import com.mongodb.MongoClientSettings
import com.mongodb.async.client.MongoClients
import olon.util.{ConnectionIdentifier, DefaultConnectionIdentifier}
import org.bson.codecs.configuration.CodecRegistries

val client = MongoClients.create("mongodb://127.0.0.1:27017")

// main database
MongoAsync.defineDb(DefaultConnectionIdentifier, client.getDatabase("mydb"))

// admin database
case object AdminIdentifier extends ConnectionIdentifier {
  val jndiName = "admin"
}

val codecRegistry = CodecRegistries.fromRegistries(
  MongoClientSettings.getDefaultCodecRegistry(),
  CodecRegistries.fromCodecs(new LongPrimitiveCodec, new IntegerPrimitiveCodec)
)

val admin = client.getDatabase("admin").withCodecRegistry(codecRegistry)
MongoAsync.defineDb(AdminIdentifier, admin)