Bevy run

[TimJentzsch]

Add a bevy run command which conveniently runs your Bevy app.

It mostly wraps cargo run, but also provides a web sub command, which makes it a lot easier to target the browser.

This option will compile your app for WASM, create JS bindings, add an index.html file if you don't provide one yourself and serves the build locally to open it in your browser.
The default index.html file is mostly what we had in bevy_quickstart.

This is the last part of #24.
Closes #8.

Testing

1. Checkout the bevy-run branch.
2. Run cargo install --path . to install this version of the Bevy CLI.
3. Navigate to your Bevy app.
4. Run bevy run web.

Note that your app must be compatible with WASM. If you have features or profiles enabled by default which are not compatible with WASM, you need to disable them. E.g. bevy run --no-default-features web.
If you have a custom index.html configured for trunk, it might also not work out of the box. You can try removing the entire web folder to try the default setup.

A good example project is of course bevy_new_2d, which you can test on this branch: TheBevyFlock/bevy_new_2d#312

[BD103]

Great! I have a few nits, but feel free to merge this once you feel it is ready.

[BenjaminBrienen]

I've had situations where https on localhost was necessary for development of a project. Do you think it would be nice to have the option here?

[BD103]

In my experience, setting up HTTPS is not worth it for a development server such as this. The primary purpose of TLS is to secure communication across untrusted networks, but 127.0.0.1 is completely local, so there's no network to worry about. bevy run web is not meant for production. In those cases you build everything ahead of time and serve it with something like Nginx, which implements TLS already.

[TimJentzsch]

Is it possible to create a valid certificate for localhost to enable HTTPS?
I'd say that when we need it, we can create a follow-up issue to enable that functionality :)

[BenjaminBrienen]

Yes, assuming openssl or the like is installed. We can leave it to the user to create their own self signed cert. It's a common step for web developers and is usually its own step outside of other tooling.