Shanling Q2 port v2.1

• The screen redraws less on each page flip: only the area that changed on the previous frame is copied over, and a failed flip redraws the whole frame.
• The battery level keeps its last good reading when the gauge briefly fails to read, rather than showing 0%.
• Finishing a charge while plugged in no longer looks like an unplug; charger status is read at most once a second.

Install by unzipping rockbox.zip over .rockbox on the card; your config.cfg is kept.