Difficult to Change Settings for this library

[Legohead259]

Hi there! I have been trying to set up this library for a project. I have used the example code found in the ESP32 examples, but noticed some things that could be improved.

1. It is difficult to determine which storage system is currently being used. When first testing the "SD card" example, I could open the server and connect to it with a client (WinSCP). But, nothing was showing up. It was only after digging a bit and changing the DEFAULT_STORAGE definition to STORAGE_SD that it worked. None of the debug flags actually told me what was being used
2. Speaking of debug flags it is difficult to figure out what flags need to be defined in order for it to work as intended. I think a section at the top of FtpServer.h that can be commented/uncommented as needed would be beneficial (if this is already included, perhaps better highlighting would be prudent as I couldn't find anything)
3. When experimenting if I could change the storage type for the FTP server without changing anything in the library files, I noticed that if the definitions are redefined in the main example a compiler warning is issued and the change is not implemented. I tried both before and after the #include <FtpServer.h> call, but neither worked.If there could be someway to modify the storage type without messing with the library files (something important in an environment where the library may be updated or deleted/re-downloaded) that would be excellent!

Thanks,