FIX: Move up comment related to test coverage into its section.
BREAKING CHANGE: JSONbig is not anymore the default json serializer/deserializer, native JSON lib is used instead.

In order to use the JSONbig serializer/deserializer, initialize the client with bigint to true i.e solr.createClient({ bigint : true}) or via client.options.bigint = true. The reason for this change is that JSONbig has a significant performance impact when manipulating "large" chunk of data.