ENH: Add input validation for app name

Author: jamesobutler

hooks/pre_gen_project.py

@@ -0,0 +1,15 @@
+import re
+import sys
+
+APP_NAME_REGEX = r"^[a-zA-Z0-9]+$"
+
+app_name = "{{ cookiecutter.app_name }}"
+
+if not re.match(APP_NAME_REGEX, app_name):
+    print(
+        f"ERROR: {app_name} is not a valid app name. "
+        "Only alphanumeric characters are allowed."
+    )
+
+    # exits with status 1 to indicate failure
+    sys.exit(1)