How to debug json's set to mining pool
**Describe the bug**
I wanted to debug print out the json's sent to the mining pool.

**To Reproduce**
I added this code to `EthStratumClient::subscribe`
```cpp
  JsonRequest::create(doc, m_sequence, "mining.subscribe", params);

  StringBuffer buffer;
  Writer<StringBuffer> writer(buffer);
  doc.Accept(writer);
  LOG_INFO(buffer.GetString());
  ```

**Expected behavior**
To see the json printed out by the logger.

**Required data**
 - XMRig version
    - master
