move tile unit/pixel/meter helpers to Geo & Style modules
move base URL finder into function
add URL cache-busting for worker, layers, styles
move tile set tracking into functions
layer visibility can be turned off in the stylesheet
move tile DOM updates to own function
add ability to rebuild tile geometry on the fly (for example, to change styles)
generalizes the geometry processing/build process in the web worker to work for both
the initial tile load case, and subsequent "rebuild" requests
make tile rebuild also work for canvas renderer