Allow optional _parameters with default values and enable T->string conversion using T.fronStrimg().
* cache.d: Created this CacheSessionStore as a hot cache that allows
  faster fetching of recently used data

* memory.d: Added the hot cache for faster fetch
Changed from Variant to Json

* redis.d: Initial commit for Redis

* server.d: Added HTTPServerRequest.cache to load a global Session
  available in all fibers

* session.d: Changed Variant to Json to allow string conversion for
  Redis SessionStore
added SessionStoreSettings to allow multiple upcoming features to be
  selected

* web.d: Added CacheVar!(T,"key") for global session vars available in
  all fibers
Setup CacheVar! UUID support for grouped cache access rights