HTTPClient fixed timeout sending payload HTTPC_ERROR_SEND_PAYLOAD_FAILED

ESP8266HTTPClient.cpp does
```
int HTTPClient::sendRequest(const char * type, const uint8_t * payload, size_t size)
...
// transfer all of it, with send-timeout
if (size && StreamConstPtr(payload, size).sendAll(_client.get()) != size)
return returnError(HTTPC_ERROR_SEND_PAYLOAD_FAILED);

```

StreamConstPtr derives from Stream which defines
```
protected:
unsigned long _timeout = 1000; // number of milliseconds to wait for the next char before aborting timed read
```

So no matter what your HTTPClient.setTimeout is, 1 second pause on your server side causes a HTTPC_ERROR_SEND_PAYLOAD_FAILED.

It's obvious, but httpclient should create the StreamConstPtr, set its timeout to either the full or the remaining millisecs, and then issue the sendAll.