fix duplicate symbols when using with webp via pods
Updated all block params and properties, using defined blocks that have var names (for proper autocomplete). Created a  SDWebImageNoParamsBlock to distinguish easier from other no params blocks. Fixes #810
Merge branch 'master' of https://github.com/rs/SDWebImage
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
Merge branch 'master' of https://github.com/rs/SDWebImage