Fix for issue #68: decode key before list_objects

[ChinnoDog]

When listing directory contents the parent directory is enumerated and then metadata is obtained for each child object. The keys in the parent directory are URL encoded. These need to be decoded before obtaining the metadata because boto3 will URL encode them again, resulting in a double encoding.

This issue is easy to test by using scandir to obtain contents of a directory that contain file names with characters that will be URL encoded, such as spaces.