Implement Various Caching mechanisms for memoria

[0xnullifier]

Caching is important part of memoria as it takes up a notch from a simple key value store to fairly production level implementation of a key value store.

For each caching system the following CachePolicy interface must be implemented

type CachePolicy interface {
	Eject(m *Memoria, requriedSpace uint64) error
	Insert(m *Memoria, key string, val []byte) error
}

Currently the defaultCachePolicy is implemented which randomly deletes key value pairs from the cache
The following issues are opened explaining in details the cache policies to implement
FIFO Very famous cache policy it stands for First In First Out check it's issue here #13
LRU Least recently used is a great policy and would love to see this one implemented #14
CUSTOM If you have another great idea would love to listen to it open up a issue