Fixed to use general perpose.

 * Chagned digest header parmeters to digestHeaders as struct.
 * Created function for generating HA1 and HA2.
 * Changed NonceCount to const.
 * Changed hard code path to digestHeaders.Path.

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>
Fixed typo digestHeaders.

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>
Added Get() method.

 * Changed Auth() method that returns digestHeaders.
 * Added Get() method
   - That requests GET method and returns http.Response with digestHeaders.
   - Increases Nonce-Count using the same Nonce value.

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>
Fixed error handling when status code is not 200.

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>
Update to allow for Digest Auth to be able to be added to any request