#8 Declare encoding; decode response

[Marc-Antoine Parent]

The wrapper encodes unicode in UTF-8 but fails to declare it; so endpoints fail to interpret it (experienced with Joseki 3.4.2)

Also, the response should be decoded, otherwise UTF-8 data is double-encoded in resulting literals (experienced with JSON output.)

Patch provided, including changes to tests. Some of the tests were failing otherwise, and were changed. One of the tests still fails for other reasons.