LRU Cache

This is an implementation of an in memory LRU Cache!

For some example uses see main.go for some trivial examples or the tests TestCache_GetItem and TestCache_AddItem

This cache uses the Write Through policy.

Areas of improvements

There definitely can be more test cases added since caching can get quite complicated
- The test cases shown show a minimal viable cache and provide coverage for the basic cases
This cache does O(n) retrieval for the LRU. To implement a O(log(n) solution refer to the comment in this file
The code is more strict towards the current Write Through policy, so changing to a new policy would require some refactoring, though not much and I did comment where some of those changes would be like here