Issue #116 - Possible concurrency issues
Issue #170 - NPE after unmount SD card
Cache images on device's file system if SD card becomes unmounted
Fixed visibility of methods ImageLoader.denyNetworkDownloads(...) and
ImageLoader.handleSlowNetworks(...)
Made FailReason as a class instead of enum. FailReason keeps fail type
(enum) and error cause (Exception/Error).
Change of using FaileReason in switch statement: failReason ->
faileReason.getType()
Sample: Use new FailReason class
Update Readme
Built new snapshot