update get.go and can work now

get.go
+change the file from model/user.go to model/user/get.go,that will be
separate with others files and apis.the user folder noly have the file
associate with the user api
+modify the struct User in the get.go file.because the the renturn json,it
is struct like:reponse{...},not the user{...}
+change the func Get(),not work as the method of struct anymore.and it
noly take one oauth.Transport as parameter.it is more simpler