LRU eviction in case disk gets full

[swapnilgawade16]

Option to enable LRU eviction in case disk gets full.

We are evaluating nuster to be used as a http proxy to increase performance and throughput of our backend http based storage that serves immutable objects. Each object has unique path /object/UUID. It would be very useful if we can get an option to enable LRU eviction to cache new requests when allocated disk size is full. Also may be its a good option to configure the max disk-size (memory equivalent --> data-size) after which LRU can kick in.

[aleksystasiak]

Would be also great for memory cache