Beta 9: Support for resuming downloads, faster operation queue

Included in Beta 9 is one big feature and one big performance improvement:

• New support for resuming canceled downloads. If you call cancelTaskWithUUID:storeResumeData: you can specify that any data already downloaded be stored in the memory cache. If you later attempt to download the image at the URL again, it will resume where it left off. (#331) Caveats:
  • Resume data is only stored in the memory cache, not the disk cache
  • Your server must support resuming downloads by responding to requests with the Accept-Range header == bytes and providing either an ETag header or a Last-Modified header.
• Performance switch to PINOperationQueue from NSOperationQueue which turned out to take a lot of the time PINRemoteImage used on the main thread. (#338, #326, #329)

Beta 8

Included in Beta 8:

• Complete refactor of build system #317
• Some performance improvements #285 #287 #312
• Added ability to manually add image to cache #299
• Fixed GIFs #302
• Added ability to configure headers sent with requests #293
• Added ability to automatically support @2x and @3x images #311
• Updated to the latest PINCache #320

Beta 7

Included in beta 7:

• Fixes images sometimes being corrupted: #279
• Fixes cache cost calculation: #278
• Switches our CI to something more reliable: #266
• Fixes a build error for Carthage: #273
• Adds an option to bypass the cache: #272

3.0 Beta 6

On to Beta 6!

This release contains the latest PINCache and a new pluggable cache (so you can use your own cache instead of PINCache if you wish).

Beta 5

• Fixes a nasty bug in Beta 4 which made it so alternativeRepresentationProviders were ignored!
• Re-enables PINCache dependency in CocoaPods to un-break upstream dependencies. This will be re-enabled in the 3.0 final release.

Beta 4

Includes new pluggable cache, thanks @skeeet !

Beta 3

Includes PINCache 3 beta.

3.0 Beta 2

[fix] Merge tvOS spec into iOS spec [#196]

3.0 beta

3.0.0-beta

Forward port changelog

Adds progressive quality to callback

[new] Have PINProgressiveImage pass back the quality of the current progressive image #185