Time based LRU Map

[raycardillo]

We have a LruMap but we don't have a time based cache or map. The concepts are similar and it should be easy to add on top of the existing LruMap implementation but it would be good to keep them separate to avoid the extra overhead that often comes with a time based cache. Such implementations can get very sophisticated and difficult to meet every use case, but a simple practical approach would make a nice contribution that would satisfy most typical apps that just need a simple time based Map (e.g., would be useful when building a Map of ephemeral data such as Bluetooth devices or WiFi connections).

[raycardillo]

I'll be submitting a PR for this soon. Just finishing up test cases before submitting the PR.