Example URLs are ugly

[rparrett]

Here's an example of a particularly nasty looking example URL:

https://bevyengine.org/examples/ECS%20(Entity%20Component%20System)/iter-combinations/

Something like

https://bevyengine.org/examples/ecs/iter-combinations/

or

https://bevyengine.org/examples/ecs-entity-component-system/iter-combinations/

would be nicer.

This seems like an issue for this repo, but it looks like the changes required to fix this (seems potentially straightforward) must be made to the example-showcase tool in the bevy repository.