Implement LIRS page replacement algorithm

[nicoloboschi]

JIRA: https://dev.blazingcache.org/jira/browse/BLAZ-54

Reporter: alessandro.luccaroni @aluccaroni

Implement a new page replacement algorithm with improved performance over LRU: LIRS (Low Inter-reference Recency Set)

Maybe we could also evaluate a facility to easily swap between page replacement algorithm on startup (for now only LRU and LIRS)