Add maxAge option

[javi11]

Add a lazy max-age implementation that lacy removes expired items on get, peek, or has method calls. Hope the implementation fits on your library :).

Closes #18

[javi11]

Done ;). Thanks for the comments

[sindresorhus]

Can you fix the merge conflict?

[sindresorhus]

In the has() method. Boolean(cache.get(...)) is not the same as cache.has(...).

[javi11]

In the has() method. Boolean(cache.get(...)) is not the same as cache.has(...).

mm depending what we want if we want that has return true for items that has been expired we can remove that part, but if has will return false for expired elements, there is the need to get the element first to verify the expiration time :S

[sindresorhus]

Can you do a test where maxAge option is set, the value is set to undefined (which is different from no key being there), and using .has(). It looks like that will be a false-positive.

[javi11]

Done, I called the set option maxAge to options = { maxAge } and set maxAge globaly by default Infinity instead of 0 that sure it makes more sense ;)