Create hunt.caching module, using radix container.

[zoujiaqing]

Use Caffeine or JCache API (JSR 107) api design.

[zoujiaqing]

auto cache = new CacheBuilder!(String, String)() {}
    .expireAfterWrite(5.MINUTES)    // expire/refresh after 5 minutes
    .resilienceDuration(30.SECONDS) // cope with at most 30 seconds
                                              // outage before propagating 
                                              // exceptions
    .refreshAhead(true)                       // keep fresh when expiring
    .build();