a helper class for DiskLruCache(https://github.com/JakeWharton/DiskLruCache)
you can create DiskLruCache more easily by using DiskLruCacheHelper. what's more,it providers a series of static method to read/write/asynchronous write/remove cache. for example,if you want to write cache to Bitmap,just call DiskLruCacheHelper.writeBitmapToCache(),never need to call DiskLruCache.edit()、commit() and so on.there are some another useful methods like getDiskCacheDir()、getAppVersion（）...
##in a word,mom won't worry about my study when using DiskLruCacheHelper:)