Update to AFNetworking 2.0

Fetching the podcast feed and downloading episodes now use NSURLSession which involved quite a lot of change in the network code.
Update AFNetworking to 2.0.1

Signed-off-by: Tom Diggle <tom@tomdiggle.com>
Refactor background refresh

Signed-off-by: Tom Diggle <tom@tomdiggle.com>
Change only show notes button uses tag

Signed-off-by: Tom Diggle <tom@tomdiggle.com>
Refactor postNotification: method

Signed-off-by: Tom Diggle <tom@tomdiggle.com>
Fix Now playing button gets removed when playback has ended or failed

Signed-off-by: Tom Diggle <tom@tomdiggle.com>
Change now doesn't reload the media that is already playing

Signed-off-by: Tom Diggle <tom@tomdiggle.com>
Change it is recommended to use copy for NSString

Signed-off-by: Tom Diggle <tom@tomdiggle.com>
Change audio player now always displays the hour digit

Signed-off-by: Tom Diggle <tom@tomdiggle.com>
Update docs

Signed-off-by: Tom Diggle <tom@tomdiggle.com>
Remove duplicate image tag

Signed-off-by: Tom Diggle <tom@tomdiggle.com>
Bump to version 2.0b3

Signed-off-by: Tom Diggle <tom@tomdiggle.com>