Async version of the TkinterMapView widget

[alex-schulster]

What?

This PR adds the implementation for an async version of the TkinterMapView widget (called AsyncTkinterMapView).

Why?

If willing to use this widget in an application that makes use of async tasks rather than threads, the original threaded version won't work. See issue #151.

How?

The implementation is basically a copy of the original class with every thread replaced by async actions. This is not pretty, but it works fine for basic usage. A basic example using this implementation is provided.

[mke21]

Nice work, only remark: You forgot to update the requirements. You are using aiohttp but it's not installed with the requirements.txt nor with the setup.py.

[alex-schulster]

Oops, you're absolutely right. This is now fixed. Thanks for the insight.

[mke21]

Nice, now hopefully this will be merged. But alas the project seems to be very dormant, seeing all the open pull requests here.

[stevej2608]

I've tried this PR with the accompanying demo async_map_view_demo.py and it works fine.

Running the same demo with customtkinter substituted for tkinter fails with no error report.

import customtkinter

...

root_tk = customtkinter.CTk()

...

async_mainloop(root_tk)

The examples/map_with_customtkinter.py demo also fails when using AsyncTkinterMapView.