Changes:
1. Refactoring and some cleanup of JWT handling code:
* Instead of caching AuthResult cache decoded claims (which signature was verified). Validating claims and determining role is done after cache lookup
* Cleaned up API so that usage of it is simplified: lookupJwtCache cache key >>= parseClaims configJwtAud time
* Handling of JwtCacheState initialization and updates of configuration is encapsulated in Auth.JwtCache module
2. Generic high performance (hopefully) scalable, dynamically resizeable cache implementation based on stm, stm-hamt and sieve algorithm. It also integrates with PostgREST measurements infrastructure providing usage stats (ie. hit ratio, evictions count)
