drscheme:language:add-snip-value in DrScheme Tools Functions

• (drscheme:language:add-snip-value test-value convert-value setup-thunk) -> void?
     test-value : (any/c . -> . boolean?)
     convert-value : (any/c . -> . (is-a?/c snip%))
     setup-thunk = void : (-> any/c)

  Registers a handler to convert values into snips as they are printed in the REPL.

  The test-snip argument is called to determine if this handler can convert the value and the convert-value argument is called to build a snip. The (optional) setup-thunk is called just after the user's namespace and other setings are built, but before any of the user's code is evaluated.

  All three functions are called on the user's thread and with the user's settings.