Add more control on `maxAge` eviction

Hello, The rule maxAge being checked only on get calls is a bit restrictive to me. In my use case. I use peek to select some elements and then I really use only some of them and call get.

In this way, I keep the last used date accurate to evict the oldest when max is reached. Now most of my elements are never accessed using get and maxAge is not triggered.

What do you think about adding a method to check availability or adding a parameter to get or peek to control maxAge eviction?

It would prevent me for doing this:

// Check manually if the peer is active
if (peers.maxAge && (Date.now() - peers.cache[peerId].modified) > peers.maxAge) {
  peers.remove(peerId)
  continue
}
// Don't mark the peer as most recently used on announce
var peer = this.peers.peek(peerId)

I can propose a PR in this way if you want to.

[mafintosh]

i’m gonna release this + the .keys thing as a major bump since its technically changing behaivor

[yciabaud]

Thank you for your reactivity, making peek respect maxAge fixes my issue. I was not sure this was not the expected behavior of peek.