Corrected getSupportedCurrencies to use an array

Corrected getSupportedCurrencies to use an array instead of
a dictionary.

Also changed CBResponseHandler so the result parameter is of
type id instead of NSDictionary pointer, as not all of the coinbase API
returns JSON.
Corrected CBResponseHandler

CBResponseHandler should just be an id, not pointer to an id.
Merge pull request #3 from sirnacnud/master

Corrected getSupportedCurrencies to use an array