Added LRUCache todo.
Added LRUCache todo.

It may be that the speedups we've implemented already are sufficient in the real world, but it's worth noting that there is an alternative.

appleseedhq/cortex,lento/cortex,goddardl/cortex,goddardl/cortex,hradec/cortex,goddardl/cortex,hradec/cortex,appleseedhq/cortex,hradec/cortex,appleseedhq/cortex,lento/cortex,lento/cortex