fix duplicate symbols when using with webp via pods
guarding against image source == NULL
Merge pull request #819 from n13/master

guarding against image source == NULL
Added test for the UIImage+MultiFormat crash
Fixed SDWebImageCombinedOperation cancel crash (#798 #809)
Merge pull request #795 from xlchen/master

fix duplicate symbols when using with webp via pods
Add a weak NSMapTable-based memory cache. This allows the cache to reference previously cached object that are still alive and reuse them instead of redownloading them or pulling them out of the disk cache. This is faster and uses less memory.
user more concise initializer
Merge branch 'master' of github.com:dimavartanian/SDWebImage