CacheSerializer with direct access to DiskLruCache stream

[blazeroni]

Currently, CacheSerializer forces everything to be a String. This can be inefficient for data that is not naturally a String since it requires creating a String just to store the data, particularly if no ram serializer is used. However, DiskLruCache exposes streams that can be used directly to write data. It would be helpful to allow a version of CacheSerializers which can use these streams.