Suggestion for SD library

Hello

I would suggest adding a function call SD.end() to the SD library. This would serve the same purpose as Serial.end() does on Serial connection. Basically a shutdown command for the SD card (and library).

Reason for this would be an ease of use and coding for projects that require swapping SD cards on the fly without powering down the Arduino. At the moment the current SD library doesn't like when the card is initialized, removed, reinserted and reinitialized (with the same or different card).

Thank you in advance.