documented workaround for frameworks that extend optional libraries
refs #620 move NSData+ImageContenttype to the SDWebImage subdirectory
Merge pull request #624 from akhenakh/620_move_categories

refs #620 move NSData+ImageContenttype to the SDWebImage subdirectory
SDWebImageDownloaderOperation: pass orientation to initWithCGImage during progressive rendering
Merge pull request #633 from hlian/progressive-orientation

SDWebImageDownloaderOperation: pass orientation to initWithCGImage during progressive rendering
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