add texture UV generation for polygon (flat and extruded) geometry builders
add texture UVs to polygon render style and shaders
update build
add texture UVs to polyline geometry builder
add texture UVs for lines to polygon render style
dynamically adapt vertex layout for polygon render style so that texture coords are only added when needed
if texcoords option was not passed, there's no need to waste space on them
move axis-aligned bounding box calc to a utility function
add test for polygon bounding box calc
move test polygon data to fixture
merge master
Merge pull request #34 from tangrams/texcoords

Add texture UVs to geometry builders