Market & API Key Updates

v0.2.0 introduces the latest changes to the Market endpoints. Like in the API, the price & history endpoints have been merged, and the search parameters have been expanded.

Your API key is now properly provided with the new private_key param, and requires no change to your application code, but you may need to update the value to your new account-based API key.

A couple of deprecated endpoints have also been removed from the library.