Ebaysdk

- added response_obj() which turns a dict into a Struct
e.g. { a : { 'name' : 'tim' } } can be accessed like a.name
- add support to dict args in the execute call. execute will now check the
data type and convert to xml if necessary
- clean doctests

- moved from httplib to pycurl
* pycurl was chosen because of its https/proxy support and
that it's thread-safe.

- fix escape username/password
- fix error handling
- cleanup doctests

- fix download link