Modified the cost calculuations to appropriately compute the 'scale' of an image
fix #610
Adds setter to override default SDWebImageDownloaderOperation.
atomicity was implicit (compiler complained). Declared 'nonatomic' as that's fairly standard on iOS
Updated code sample to not use deprecated api
Merge pull request #890 from kyleclegg/master

Updated key filter sample code
minor spelling (forth->fourth)
Merge pull request #893 from asparagui/sp_fixes

minor spelling (forth->fourth)
Update UIImageView+WebCache.m

Can cause animation losing or crash if you are in a thread.
Switch to built in XCTest async
Fixed #900 by adding a new flag SD_LOG_NONE that allows silencing the SD logs from the Prefetcher
Merge pull request #896 from skrew/master

Update UIImageView+WebCache.m
Handle empty urls NSArray

In some cases the user may end up with an empty urls NSArray, in which case the completion block is never called.
This commit handle such case to call immediately the completion block (if any)
Merge pull request #929 from kirualex/patch-2

Handle empty urls NSArray
Decoding webp, depends on source image data alpha status.
Implement 'SDWebImageDownloaderAllowInvalidSSLCertificates' option.
Fixed #774 - remove deprecated methods. Since 4.0 is a major release, we don't need the backwards compatible methods
Merge pull request #937 from pavelosipov/master

Implement 'SDWebImageDownloaderAllowInvalidSSLCertificates' option.
Merge pull request #936 from flexih/master

Decoding webp, depends on source image data alpha status.
Merge pull request #898 from mattjgalloway/xctest_async

Switch to built in XCTest async