Add draw_shape and draw_shapes with tests

draw_shape turns 360 divided by the number of sides after each side and rejects
fewer than 3 sides. draw_shapes draws a triangle up to a decagon, each in a color
from the palette.

Task: MIL-003#3
Task: MIL-003#4
Task: MIL-003#5

src/turtle_challenges/__init__.py

@@ -3,17 +3,21 @@
 @brief Solutions to the turtle graphics challenges of day 18 of Udemy's
 100 Days of Code.
 
-The challenges so far are @ref turtle_challenges.square.draw_square and
-@ref turtle_challenges.dashed_line.draw_dashed_line. Each takes the turtle as its
+The challenges so far are @ref turtle_challenges.square.draw_square,
+@ref turtle_challenges.dashed_line.draw_dashed_line and
+@ref turtle_challenges.shapes.draw_shape. Each takes the turtle as its
 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.shapes import draw_shape, draw_shapes
 from turtle_challenges.square import draw_square
 
 __all__ = [
     "draw_dashed_line",
+    "draw_shape",
+    "draw_shapes",
     "draw_square",
     "random_color",
     "random_palette_color",