Sketching repl

[soegaard]

Idea:

Make a language mode that doesn't open a separate window,
but displays the "current bitmap" in the repl.

Notes:

• the update loop should be disabled (as default)
• only display the bitmap, when a drawing function is called
  [or simply compare the bitmap before and after each evaluation to see whether
  it needs to be displayed in the repl again]
• alternativ: a plugin for DrRacket could have a static canvas to draw on