Added SDL based audio example.

[libesz]

Earlier SDL crate versions were not able to initialise more than once, but now user can also use SDL to produce audio, not only to create windows and display content. Audio related embedded project may see this as a benefit, to be able to run the audio engines on simulator without much modification.

Thank you for helping out with embedded-graphics-simulator development! Please:

• Check that you've added passing tests and documentation
• Add an example where applicable
• Add a CHANGELOG.md entry in the Unreleased section under the appropriate heading (Added, Fixed, etc) if your changes affect the public API
• Run rustfmt on the project
• Run just build (Linux/macOS only) and make sure it passes. If you use Windows, check that CI passes once you've opened the PR.

PR description

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[rfuest]

Looks good, expect for a few nits and some missing comments.

[libesz]

Thanks for the review. I think I addressed all comments.
Is there a way I can fix the stable build, or can we just ignore it?

[rfuest]

A few more suggestions.

Is there a way I can fix the stable build, or can we just ignore it?

Don't worry about that in this PR. At some point this repo needs to be migrated from CircleCI to GitHub Actions, at which point it would be easier to bump the MSRV for this crate to fix the build. But the same error has showed up elsewhere before and might need some further investigation.

[rfuest]

LGTM. Thanks!