first commit, with first passing test - RemoveStartsWith implemented
created UserFixture - represents some data we want to cache
Created failing test for Get<>
implemented finding by generic<T> - issue with serializing back out of Mongo however
implemented Get<T> - used ServiceStack.Text for json serializer
removed Deserialize method from CachedItem
implemented Remove (by key)
implemented Contains (exists)
checks if item exists in cache
added dateTimeOffset to CachedItem
added dateTimeOffset to ctor of CachedItem
updated tests

Added AddTests - to test Add method of MongoDbApiOutputCache
currently failing on Expiration property
was creating a new instance of UserFixture each time.
Set to clear mongo collection each time, test now passes
(changed assertion too)