Make API logging more useful

Make the API client log out a warning whenever an HTTP 4XX or 5XX response is
received. Demote messages detailing the contents of every single request and
response from priority "info" to "debug".
> When you receive a response, Requests makes a guess at the encoding to use for decoding the response when you access the Response.text attribute. Requests will first check for an encoding in the HTTP header, and if none is present, will use chardet to attempt to guess the encoding.
>
> The only time Requests will not do this is if no explicit charset is present in the HTTP headers and the Content-Type header contains text. In this situation, RFC 2616 specifies that the default charset must be ISO-8859-1. Requests follows the specification in this case. If you require a different encoding, you can manually set the Response.encoding property, or use the raw Response.content.