Change in 'fields' UAC API parameter

To get a header's value only the name (as binary) is used, i.e. {fields, [<<"Call-Id">>]} instead of {fields, [{header, <<"Call-Id">>}]}. The response will also include the name directly: [{<<"Call-Id">>, …}] instead of [{{header, <<"Call-Id">>}, …}].

Parameter 'all_headers' has been added to the list of fields to get all headers at once
Tutorial update with the new API