documented workaround for frameworks that extend optional libraries
Update SDWebImagePrefetecher.m

I added progress block that I need.
Merge pull request #634 from burakkilic/patch-1

Update SDWebImagePrefetecher.m
Update SDWebImagePrefetecher.m

I added "+ self.skippedCount" because it never completes if there are skipped operations.
Merge pull request #635 from burakkilic/patch-1

Update SDWebImagePrefetecher.m
Missing method definition in header file
Merge pull request #637 from runmad/master

Missing method definition in header file
added clearDiskOnCompletion
Merge pull request #638 from limbo-lab/master

added clearDiskOnCompletion
Bump version to 3.5.4
Fix deployement target for arm64
Added method to SDWebImageManager to check if an image exists in either the disk OR the memory cache
add category for imageView's highlighted state
Check progressBlock is not nil before executing.
Merge pull request #647 from musaicapp/bug

Prefetcher: check progressBlock is not nil before executing.
Add typedef for cache operation complete block

Makes it cleaner when users want to define the block independantly
Merge pull request #649 from finik/patch-1

Add typedef for cache operation complete block
add support for high priority download
Merge pull request #664 from xuki/master

add support for high priority download
Fix some indentation issues