added test case which tests to see if JSON was returned if no Accept header was provided
If no ACCEPT header is provided in the HTTP Request, application/json will be used as the default
added test cases to replicate #11 (server crashes if no JSON data in a POST)
caught value error thrown if illegal json was provided in post requests, fixing issue #11

instead of crashing server, the bad request now triggers a 400 BadRequest response
PEP8 formatting
now get_response in tests will parse based on the response's content type
Merge branch 'master' into pr/17
Merge branch 'master' into pr/18
PEP8 fixes