Issue #24

I've left the javadoc pretty thin for the moment.  I've also avoided mentioning how these operations might or might not interact with eviction/expiration - that will however need addressing in the future.  If you think I should address that now then let me know.  Like the basic CRUD ops we going to stick with these standard versions and look in to adding "slimmer" versions with simpler return types if they are found to be necessary.