some experiments
use short vertices, add docs
prefetch parent tiles
cleanups
theme tweaks
use separate locks for nodes/ways/areas render instructions cache
add null check
it probably makes no sense to cycle ByteBuffers for upload to GL
- use Stencil instead of Depth for clipping test
  to avoid drawing everything with polygonOffset
- add GLState.useProgram
add field for checking if labels are joined with neighbours
cleanups
refactor loops
no need to buffer outputstream here
limit TextItem pool items
use void pointers
some more labeling experiments