Avoid equality tests in examples, and use approx otherwise

[Ogeon]

Floating point numbers are crazy and should not be trusted. They should therefore not be compared in the examples (for aesthetic reasons) and any unit test that compares them should make use of the approx crate.

[sidred]

Should be closed by #51

[Ogeon]

There are still some examples where regular equality is used (https://ogeon.github.io/docs/palette/master/palette/trait.GetHue.html for example), so this issue stays as a reminder until all of them has been changed.