I also made some minor changes to `plot' so that its functions would
type more easily. In particular, everything that used to take a list
of vectors now accepts a (Sequenceof (Sequenceof Real)). The 3D
discrete histogram renderers now also accept lists as well as vectors
in the sequence of categories.
For now, in typed/plot functions, optional non-keyword arguments are
required. As soon as Vincent closes PR 13354, I should be able to
uncomment part of a macro in "typed/plot/syntax.rkt" to make them
correctly optional.
