Fix for info() failing with the new HTTP API format. Added test.

[SteveTherrien]

Changes:

curl_setopt($ch, CURLOPT_POSTFIELDS, \json_encode($params));

to

curl_setopt($ch, CURLOPT_POSTFIELDS, \json_encode((object)$params));

so that an empty array gets encoded as {} instead of [], allowing parameter-less API calls (like info()) to produce a valid JSON payload.

Fixes #64

[FZambia]

Thanks a lot @SteveTherrien !