Update documentation and code snippets

docs/code_snippets/quickstart/calculator_app.py

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+import operator
+import re
+
+from argenta import App, Orchestrator, Response, Router
+from argenta.app import DynamicDividingLine
+from argenta.command import Command, Flag, Flags
+from argenta.response.status import ResponseStatus
+
+router = Router("Calculator")
+
+operations = {
+    'mul': operator.mul,
+    'sub': operator.sub,
+    'add': operator.add
+}
+
+@router.command(
+    Command(
+        "calc",
+        description="Calculator with two numbers",
+        flags=Flags(
+            [
+                Flag("a", possible_values=re.compile(r"^\d{,5}$")),  # First number
+                Flag("b", possible_values=re.compile(r"^\d{,5}$")),  # Second number
+                Flag("operation", possible_values=["add", "sub", "mul"]),  # Operation: add, sub, mul
+            ]
+        ),
+    )
+)
+def calc_handler(response: Response):
+    # Get flag values
+    a_flag = response.input_flags.get_flag_by_name("a")
+    b_flag = response.input_flags.get_flag_by_name("b")
+    op_flag = response.input_flags.get_flag_by_name("op")
+
+    # Check that all flags are provided
+    if response.status != ResponseStatus.ALL_FLAGS_VALID or not all([a_flag, b_flag, op_flag]):
+        print("Error: must specify --a, --b and --op")
+        return
+
+    a = float(a_flag.input_value)
+    b = float(b_flag.input_value)
+    operation = op_flag.input_value
+
+    try:
+        result = operations[operation](a, b)
+    except ZeroDivisionError:
+        print("Can't divide by zero")
+    else:
+        print(f"Result: {result}")
+
+
+app = App(
+    initial_message="Calculator",
+    repeat_command_groups_printing=False,
+    prompt=">> ",
+    dividing_line=DynamicDividingLine("~"),
+)
+orchestrator = Orchestrator()
+
+
+def main():
+    app.include_router(router)
+    orchestrator.start_polling(app)
+
+
+if __name__ == "__main__":
+    main()