Lastfm authentication procedure helpers

Basically, lastfm provides 3 ways to authenticate user:

• web application - http://www.last.fm/api/webauth
• desktop application - http://www.last.fm/api/desktopauth
• modile application - http://www.last.fm/api/mobileauth

Note that you can use any of them in your application despite their names

How to get session key for yourself for debug with GHCi:

>>> import Network.Lastfm
>>> import Network.Lastfm.Authentication
>>> :set -XOverloadedStrings
>>> con <- newConnection
>>> lastfm con $ getToken <*> apiKey "__API_KEY__" <* json
Right (Object (fromList [("token",String "__TOKEN__")]))
>>> putStrLn . link $ apiKey "__API_KEY__" <* token "__TOKEN__"
http://www.last.fm/api/auth/?api_key=__API_KEY__&token=__TOKEN__
>>> -- Click that link ^^^
>>> lastfm con $ sign "__SECRET__" $ getSession <*> token "__TOKEN__" <*> apiKey "__API_KEY__"  <* json
Right (Object (fromList [("session",Object (fromList [("subscriber",String "0"),("key",String "__SESSION_KEY__"),("name",String "__USER__")]))]))