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

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

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