Improve examples

[koalatux]

I'm not sure if the examples should be explicitly included or excluded from the workspace, but with the originally provided Cargo.example.toml the examples can't be built.

I disabled rtt in Embed.toml for the usb examples, because they don't use this crate.

The rest is just some minor cleanup.

[jonas-schievink]

Thanks!

bors r+

[bors[bot]]

Build succeeded:

• ci