2D vector code

[David Feuer]

My SVG polygon code uses 2D vectors ( (x,y) pairs ) a good bit.  Does
LilyPond already have basic functions (addition, subtraction,
multiplication by a scalar, dot product, cross product, ...) for
vectors I can use?  If not, I think I should probably write them as a
separate module.  If I write them as a separate module, should vectors
be pairs (convenient), or should they be SRFI 9 records (pretty)?

David Feuer