WebExtensions: browser.storage wrapper with expiration

[fregante]

In Refined GitHub we'd like to cache some values and currently (ab-)use local cookies to do so, but the space is so little it's barely worth caching anything more than small data: refined-github/refined-github#1529

Another example where it could be useful: npmhub/npmhub#81

LRU or expiration date would be good, as long as it doesn't need to retrieve the whole cache object at once + edit it + save it. It would be pretty inefficient on large caches.

How would you deal with this?

Related: https://github.com/SamVerschueren/map-age-cleaner

[fregante]

Done: https://github.com/bfred-it/webext-storage-cache