Merge branch 'master' into v8
# Conflicts:
# Sources/Cache/DiskStorage.swift
# Sources/Cache/ImageCache.swift
# Sources/General/KFOptionsSetter.swift
# Sources/General/KingfisherManager.swift
# Sources/Networking/ImagePrefetcher.swift
# Sources/Networking/RedirectHandler.swift
# Tests/KingfisherTests/ImageExtensionTests.swift