add a way to debug print vectors (their initial contents)
add a way to debug print vectors (their initial contents)

(Not all their contents in case they are huge, but
they are used in polygon_collision_detection.hpp for
vertices, which is often a pretty short and interesting
usage.)

idupree/Lasercake,idupree/Lasercake,idupree/Lasercake,Lasercake/Lasercake,elidupree/Lasercake,idupree/Lasercake,Lasercake/Lasercake,Lasercake/Lasercake,Lasercake/Lasercake,idupree/Lasercake,elidupree/Lasercake,idupree/Lasercake,idupree/Lasercake,elidupree/Lasercake,elidupree/Lasercake,elidupree/Lasercake,Lasercake/Lasercake,elidupree/Lasercake,elidupree/Lasercake