fixes queries for names with slashes, and adds the json query option

In order to query for names with slashes, they must be double-encoded to go through the API. Also, many queries where having issues because the format wasn't specified as JSON, which was causing some unwanted html responses (i.e. artists that don't exist that have periods in there names).

I also added cassettes for artists with slashes and periods in there names and updated the existing cassettes with the newest data.