adding type annotations for adafruit_turtle.py

Author: rrahkola

.gitignore

@@ -32,6 +32,12 @@ __pycache__
 # Sphinx build-specific files
 _build
 
+# MyPy-specific type-checking files
+.mypy_cache
+
+# pip install files
+/build/
+
 # This file results from running `pip -e install .` in a local repository
 *.egg-info