Function streamOpen

esp_duck/spiffs.cpp:151–155

    }

    void streamOpen(String fileName) {
        streamClose();
        streamFile = open(fileName);
        if (!streamFile) debugln("ERROR: No stream file open");
    }

    void streamWrite(const char* buf, size_t len) {
        if (streamFile) streamFile.write((uint8_t*)buf, len);