Return the HTTPResponse instead of pre-parsed data in request()

[demianbrecht]

Backwards incompatible

Currently, parsers are optionally passed in to pre-parse response data. This should really just pass back the raw response as pointed out in #13. This will remove the complexity of parsing the response data and put the onus on the calling code (which is where it really should be), but will also allow the caller to handle response headers, something that is currently not possible.