remove triangle subdiv fns (migrated to core.utils), rename t/centroid* fn
add int coercions for case
add tessellate-tri-with-midpoints (migrated & renamed from triangle ns)
mirgrate intersection fns from core.utils into new core.intersect ns
update intersection references in various namespaces
update/refactor tetrahedron impls, add PFaceAccess, PSubdivide & PRotate, update PTessellate to return raw faces
add test folders to tangle-all.sh
migrate tetrahedron isec into core.intersect ns