Add option to continue download in background
Provide background option through the manager
Merge pull request #534 from pixable/ios-background

iOS Background: Provide background option through the manager
Fix link to "Who Uses SDWebImage" wiki page
Merge pull request #537 from raylillywhite/patch-1

Fix link to "Who Uses SDWebImage" wiki page
Update argument list for example in README
Merge pull request #539 from sibljon/patch-1

Update argument list for example in README
Use UIImagePNGRepresentation to preserve transparency
Only perform `NSLog` statements if `SD_VERBOSE` is defined
Merge pull request #551 from robertmryan/master

SDWebImagePrefetcher should only perform `NSLog` statements if `SD_VERBOSE` is defined
Merge pull request #552 from garnett/master

Use UIImagePNGRepresentation to preserve transparency (fix for #545)
Added SDWebImageOption to enable Cookies Handling.
Merge pull request #553 from danpe/master

Added SDWebImageOption to enable Cookies Handling.
Allow setting a custom memory cost limit for the in-memory NSCache. This can help to keep memory down before memory warnings are sent by the device.
NSInteger -> NSUInteger, add getter method
Merge pull request #556 from JoshuaGross/master

Allow setting a custom memory cost limit for the in-memory NSCache.
up version 3.5 in podspec to be consistent with latest
Merge pull request #558 from shifu/master

up version 3.5 in podspec to be consistent with latest
Add HTTP header filter to pick headers for downloading request
Merge pull request #514 from crazytonyli/header-picking

Add HTTP header passing test to pick header for downloading request