fix flickering map (no visible tiles for one frame) in case tiles changed but position does not
smoother fling
add BufferObject utility functions
comment out unused stuff
back to taxicab distance
no need for polygonoffset 'factor', clip quad is always flat
comments + cleanups
make Layer.cleanup public
improve GridOverlay, keep TextLayer to not create new Canvas on each update
use theme priority(for tag group) also for node labels
print center tile of MapPosition
document MapViewPosition.getViewBox
move MapScaleBar to overlays
add OpenScienceMap protocol definition