Also, use keywords for `make-pen' and `make-brush'.
Adding `make-pen' and `make-color' creates many conflicts among
teaching libraries, such as `2htdp/image'. These are easy to fix
up in the tree, but adding such obvious names to `racket/draw'
may create other compatibility problems, so we might have to reconsider
the names.
In consultation with Asumu.
coordinates, or not, depending on the arity of that function. This
enables one to write a simple function from color -> color and
immediately map it on an image. For the situation in which the
function is location-dependent, one can still write a function from
x,y,color -> color and map this on the image.
Added test cases for these to map-image-bsl-tests.rkt.
Modified an error message from colorize, and its test cases.
Added map-image/extra and build-image/extra functions.
