Create permanent cache helper function

can you add a helper function which returns something which caches forever (IE the ttl's are max int? or something else clever). This helper function should just return a function which is basically a wrapper around .get()

Added cachedForever() helper that returns a function wrapping .get() with maximum TTL values, effectively caching forever.

include the same warning about when not to use this
Edited cached-value.ts
+4

Done, added the warning about not using this for temporary/short-lived caches.