Feature/serve pyodide locally

[berinhard]

Fixes #148

[berinhard]

For some unknown reason, the same target_sketch.js code works locally as expected, but Pyodide sketches are not running in the local web editor. They keep raising an error when calling async main():

Uncaught SyntaxError: await is only valid in async functions, async generators and modules

I'm not sure what's causing this issue, but any JS help here would be helpful. Here's how to reproduce this:

1. pip uninstall pyp5js
2. pip install git+https://github.com/berinhard/pyp5js.git@feature/serve-pyodide-locally
3. Create and compile a new sketch which uses CDN: pyp5js new online; pyp5js compile online;
4. Create and compile sketch that runs offline: pyp5js new offline --local; pyp5js compile offline;
5. Make sure you can see the results from the local version by cd to the sketch dir (where is both online.py and index.html files) and run python -m http.server. When you access http://localhost:8000/` you should see the same sketch behavior for both online and offline version;
6. Run the server with pyp5js serve --debug and try to access the 2 sketches. Both should raise the error above.

[berinhard]

Updates on the JS issue. After using addEventListener (via 7f33220) to execute the main entrypoint, the local python server version keeps working, but the web editor doesn't. But now, the error changes to:

Uncaught (in promise) ReferenceError: loadPyodide is not defined
    main http://localhost:5000/sketch/offline/target/target_sketch.js:1688
    <anonymous> http://localhost:5000/sketch/offline/target/target_sketch.js:1704
    EventListener.handleEvent* http://localhost:5000/sketch/offline/target/target_sketch.js:1703
target_sketch.js:1688:5
    <anonymous> http://localhost:5000/sketch/offline/target/target_sketch.js:1704
    AsyncFunctionThrow self-hosted:696
    (Async: async)
    <anonymous> http://localhost:5000/sketch/offline/target/target_sketch.js:1703

[berinhard]

The fix was to just remove the async statement from the main() call in the target sketch.