New library for PWM playback from SD cards: SimpleSDAudio

Hi
@manmachine: Hm, I thought about my quick solution and it is wrong - the issue is that the buffer is completely empty when issuing play and that play first reads a whole sector of 512 bytes from card before it starts playback again. This should lead to a fast but not gapless start. I think it will need a bigger overwork to get around this. I could think about modifying the lib to read the sectors byte-wise which will make the lib slower but more flexible. Audio processing will then become possible like gapless playback, fine-tuned playback tempo and mixing. But the lib might be then not as simple to use as now.

@meow...: Please provide more info what is working and what not. Error code of lib or just no sound? Or just no sound in bigger software project?