Improved structure

- Flask app factory instead of initializing `app` variable
- Gunicorn for production server
- Makefile: python3 -m
- .gitignore: instance dir

flaskapp/__init__.py

@@ -1,3 +0,0 @@
-"""Init file for the module"""
-
-from .app import app

flaskapp/app.py

@@ -1,20 +1,33 @@
-"""Flask web application
-main script"""
+"""Flask web application main script"""
 
+import os
+import secrets
 from pathlib import Path
 
 from flask import Flask
 
 
-root = Path('..')
-static = str(root / 'static')
-tmpl = str(root / 'templates')
+def create_app() -> Flask:
+    """Flask app factory function"""
 
-app = Flask(
-    '${REPO_NAME_SNAKE}',
-    static_folder=static,
-    template_folder=tmpl,
-)
+    root = Path('..')
+    static = str(root / 'static')
+    tmpl = str(root / 'templates')
 
-if __name__ == '__main__':
-    app.run()
+    app = Flask(
+        __name__,
+        static_folder=static,
+        template_folder=tmpl,
+        instance_relative_config=True,
+    )
+    app.config['SECRET_KEY'] = os.getenv(
+        'SECRET_KEY',
+        secrets.token_hex(32),
+    )
+
+    try:
+        os.makedirs(app.instance_path)
+    except OSError:
+        pass
+
+    return app