Add support for multiple file uploads

Signed-off-by: Martin Abente Lahaye <martin.abente.lahaye@gmail.com>
Check for all HTTP possible success codes

Signed-off-by: Martin Abente Lahaye <martin.abente.lahaye@gmail.com>
Use == rather than is for comparison

- is should be used for identity comparison
- tiny_url returns unicode string and python 2.x uses str by
   default. Here, the value is same, but identities are different

Signed-off-by: Martin Abente Lahaye <martin.abente.lahaye@gmail.com>