Replace ParticleEffectBundle with #[require] for ParticleEffect

[kim-fg]

Completely removes the ParticleEffectBundle struct and replaces it with #[require(...)] for all required components.
All tests succeed after changing the usage to spawning ParticleEffect directly.

fixes #418

(I also attempted to update the inline docs, but cant verify tests since DocTests simply wont run on my machine..)

[kim-fg]

All of the examples as well as the readme have been updated to not use or refer to ParticleEffectBundle. All of the examples have been ran since and seem to be acting identically to before the changes.
This PR should be mergeable now as far as im concerned.

[djeedai]

There's not a 1:1 mapping between the bundle ("components which are generally useful") and the require mechanism ("mandatory components").

[djeedai]

This is wrong, properties are optional

[djeedai]

This is wrong, Transform is not used.

[djeedai]

I think one of those might be wrong, it's not used.

[kim-fg]

There's not a 1:1 mapping between the bundle ("components which are generally useful") and the require mechanism ("mandatory components").

I understand what you mean, I can see how I made these changes without fully thinking it through.
However I don't understand, for example, how Transform can be "generally useful" and at the same time "not used".
Either way, if this is not a wanted merge then you may of course close the PR and the linked issue.

(My stance is still that suggesting the use of the Bundle system is a bit confusing, but I'm not too attached.)