Retrieves the contents of url and places it in filename. The
return value is a tuple consisting of a local filename and either a
mimetools.Message object containing the response headers (for remote
URLs) or None (for local URLs). The caller must then open and read the
contents of filename. If filename is not given and the URL
refers to a local file, the input filename is returned. If the URL is
non-local and filename is not given, the filename is the output of
tempfile.mktemp() with a suffix that matches the suffix of the last
path component of the input URL. If reporthook is given, it must be
a function accepting three numeric parameters. It will be called after each
chunk of data is read from the network. reporthook is ignored for
local URLs.
If the url uses the http: scheme identifier, the optional
data argument may be given to specify a POST request
(normally the request type is GET). The data argument
must in standard application/x-www-form-urlencoded format;
see the urlencode() function below.
