remove 'authorization_code' example

In the end, there's not much reason why this example should exist.  The
code is there for completeness but obviously, it is wrong to use the
library as is in a public setup. When dealing with client applications,
the 'implicit' flow ought to be the way to go and therefore, it's better
to advertise this only.

README.md

@@ -122,104 +122,6 @@ getUserProfile endpoint token =
 ```
 
 
-### Usage (Authorization Code Flow)
-
-A complete example is available
-[here](https://truqu.github.io/elm-oauth2/examples/authorization_code)
-(with the corresponding sources [here](https://github.com/truqu/elm-oauth2/tree/master/examples/authorization_code))
-
-
-##### Imports
-```elm
-import OAuth
-import OAuth.AuthorizationCode
-```
-
-##### Authorizing & Authenticating
-
-```elm
-update : Msg -> Model -> ( Model, Cmd Msg )
-update msg model =
-    case msg of
-        NoOp ->
-            model ! []
-
-        Authorize ->
-            model
-                ! [ OAuth.AuthorizationCode.authorize
-                        { clientId = "clientId"
-                        , redirectUri = "redirectUri"
-                        , responseType = OAuth.Code -- Use the OAuth.Code response type
-                        , scope = [ "whatever" ]
-                        , state = Nothing
-                        , url = "authorizationEndpoint"
-                        }
-                  ]
-
-        Authenticate res ->
-            case res of
-                -- Http request didn't go through
-                Err err ->
-                  model ! []
-
-                -- Token received from the server
-                Ok { token } ->
-
-```
-
-##### Parsing the token
-
-```elm
-init : Navigation.Location -> ( Model, Cmd Msg )
-init location =
-    let
-        model = {}
-    in
-        case OAuth.AuthorizationCode.parse location of
-            -- A token has been parsed 
-            Ok { code } ->
-                let 
-                    req =
-                        OAuth.AuthorizationCode.authenticate <|
-                            OAuth.AuthorizationCode
-                                { credentials = { clientId = "clientId", secret = "secret" }
-                                , code = code
-                                , redirectUri = "redirectUri"
-                                , scope = [ "whatever" ]
-                                , state = Nothing
-                                , url = "tokenEndpoint"
-                                }
-                in
-                    model [ Http.send Authenticate req ]
-
-            -- Nothing to parse, unauthenticated
-            Err OAuth.Empty ->
-                model ! []
-
-            -- An other type of error (invalid parsing or an actual OAuth error) 
-            Err _ ->
-                model ! []
-```
-
-
-##### Using the token
-
-```elm
-let
-    req =
-        Http.request
-            { method = "GET"
-            , body = Http.emptyBody
-            , headers = OAuth.use token [] -- Add the token to the http headers
-            , withCredentials = False
-            , url = "whatever"
-            , expect = Http.expectJson decoder
-            , timeout = Nothing
-            }
-in
-    { model | token = Just token } ! [ Http.send handleResponse req ]
-```
-
 ### TroubleShooting
 
 ##### Interacting with GitHub