Add random_color and the color palette

random_color returns an immutable (red, green, blue) tuple of integers from 0 to 255
and random_palette_color picks a named color. Both take an optional random.Random
so that tests can seed them.

Task: MIL-003#1
Task: MIL-003#2

src/turtle_challenges/__init__.py

@@ -8,10 +8,13 @@ The challenges so far are @ref turtle_challenges.square.draw_square and
 first argument, so it can be tested without a window.
 """
 
+from turtle_challenges.colors import random_color, random_palette_color
 from turtle_challenges.dashed_line import draw_dashed_line
 from turtle_challenges.square import draw_square
 
 __all__ = [
     "draw_dashed_line",
     "draw_square",
+    "random_color",
+    "random_palette_color",
 ]