feat: impl docs (#4)

The entire public api is covered with documentation in two languages - Russian and English.

the library now supports the latest three versions of python - 3.12, 3.13 and 3.14

minor design changes: now, when a Boolean flag is entered, its value is an empty string, not None.

tests have been adapted to the supported versions of python, readmi has been redesigned in two languages, German is no longer available.

docs/code_snippets/quickstart/simple_app.py

@@ -0,0 +1,37 @@
+from argenta import App, Command, Orchestrator, Router, Response
+from argenta.command import Flag
+
+# 1. Create app and orchestrator instances
+app = App(
+    prompt=">> ",
+    initial_message="Simple App",
+    farewell_message="Goodbye!",
+    repeat_command_groups_printing=False
+)
+orchestrator = Orchestrator()
+
+# 2. Create router for grouping commands
+main_router = Router(title="Main commands")
+
+
+# 3. Define command and its handler
+@main_router.command(Command(
+    "hello", 
+    description="Prints greeting message", 
+    flags=Flag("name")
+))
+def hello_handler(response: Response):
+    """This handler will be called for 'hello' command."""
+    name = response.input_flags.get_flag_by_name("name")
+    if name:
+        print(f"Hello, {name.input_value}!")
+    else:
+        print("Hello, world!")
+
+
+# 4. Include router to application
+app.include_router(main_router)
+
+# 5. Start application
+if __name__ == "__main__":
+    orchestrator.start_polling(app)