Update examples

This issues is intended to be a general discussion of changes to the examples we might want to make for the 0.7 release.

Candidates for removal:
- rectangle-intersection.rs
Is this an example or should this be moved into `debug-tools`? IMO it's not a great example because it mostly contains boilerplate code to make the example interactive.

Rename:
- `pacman.rs`, `progress.rs` and `analog-clock.rs`
These examples don't have a prefix, but I think they belong together because they are larger examples that don't only demonstrate a single e-g feature. Perhaps we could add a `demo-` prefix to the names, but I'm open to better suggestions.
- `hello-world.rs`?
This example would also fit in the above category, but perhaps it's better to keep the name because users might look for a hello world example.
- `input-handling.rs` -> `simulator-input-handling.rs`
- `text-fonts-signs.rs`
Is "signs" the correct word in this context? The docs inside the file use "extended characters", which would also be more appropriate for the filename IMO.

Missing examples:
- Thick triangles / polylines (#7)
- Raw image
- embedded-text
If this repo is supposed to demonstrate the whole e-g ecosystem it should also include at least one e-t example. The docs for that example could contain a link to the additional examples in the e-t repo.
- `Text` alignment
- Example that uses the return value from `text.draw(...)` to draw text with multiple styles
- Simple `TextRenderer` implementation
- Underline and strikethrough for `MonoFontStyle`