rename time => timestamp to avoid naming conflicts
add class dictionary to avoid storing strings all the time
use class ids rather than names for storing styles
reorganize properties
add interface for iterating over classproperties
even more refactoring
more refactoring and fallback values
add raster enabled/opacity
add remaining default values
names are transiton-*, not *-transition
more docs + remove StyleLayer::Ptr typedef
make more members of StyleLayer const
add way for adding/removing classes
also update child layers
move StyleLayerGroup and PropertyTransition to their own files
refactor functions
add interpolation