Initial 0.13.1 proposal

[andreyluiz]

Hello.

This PR describes a proposal to migrate the tutorial to version v0.13.1.

Here are the topics covered in this PR:

• Migration of the markdown files to v0.13.1 (sendbox #12)
• Initialization of the repo as a binary crate with examples (Transform repo into an examples crate #13)
• Not implemented yet, but update the readme file with historical versions (Docs for latest iced (and historical versions)? #1)
  • This means the current main branch would need to be pushed as v0.12.1, as you did with v0.10.0

If you like the proposal, I will continue working on this migration.

---

This is a TODO list for the migration.

• adding_widgets.md
• batch_commands.md
• batch_subscriptions.md
• button.md
• changing_displaying_content.md
• changing_styles.md
• changing_the_window_dynamically.md
• changing_themes.md
• checkbox.md
• closing_the_window_on_demand.md
• column.md
• combobox.md
• container.md
• controlling_widgets_by_commands.md
• custom_background.md
• custom_styles.md
• drawing_shapes.md
• drawing_widgets.md
• drawing_with_caches.md
• executing_custom_commands.md
• explanation_of_sandbox_trait.md
• first_app.md
• from_sandbox_to_application.md
• image.md
• initializing_a_different_window.md
• loading_images_asynchronously.md
• memoryless_pages.md
• more_than_one_page.md
• mouse_pointer_over_widgets.md
• navigation_history.md
• on_pressed_released_of_some_widgets.md
• passing_parameters_across_pages.md
• picklist.md
• producing_messages_by_keyboard_events.md
• producing_messages_by_mouse_events.md
• producing_messages_by_timers.md
• producing_widget_messages.md
• progressbar.md
• radio.md
• row.md
• rule.md
• scrollable.md
• setting_up.md
• slider.md
• space.md
• svg.md
• taking_any_children.md
• text_input.md
• text.md
• texts_in_widgets.md
• toggler.md
• tooltip.md
• updating_widgets_from_events.md
• updating_widgets_from_outside.md
• widgets_with_children.md
• width_and_height.md

[fogarecious]

Everything looks great to me! Just let me know whenever you're ready to merge the pull request.