Improve classNames JS helper example

[mbohal]

No description provided.

[bedrich-schindler]

I disagree with such change.

1. Documentation is strictly scoped to /docs dir. It's kind of standard among open-source software in Javascript word and Github as well (typically, /docs is served as Github Page). As it uses markdown, rendering engine can be easily switched to something else, easily deployed and completely disconnected from code. Maintaining documentation structure make it easy to contribute, maintain, deploy and use by different rendering engines.
2. Standard name should be js-helpers, not jsHelpers`. This is strongly connected to point 1.
3. For some reason, we use utils in the code and JS helpers in the docs. To be honest, I have always been for utils/utilities as it is common name for such functions among UI libraries. In CSS and JS. We use helpers in our personal projects. I do not like calling it jsHelpers in the code. Everything in the code is JS, it does not make sense to prefix just this. If we want to stick to helpers, call it just helpers.
4. I don't like changed documentation for classnames. We always spend time to have our examples pleasant for your eyes. This weird padding spikes my OCD. I get what you trying to achieve, but you just repeat same type of condition over and over and it does not display real life example which we try to demonstrate (?: and || / &&). So we have bad looking example with unreal example just to demonstrate few possible truthy/falsy examples, but in real life there are more not visible. If we do such exhaustive demonstration in all cases, examples would be enormous. Let's keep it simple. I

[bedrich-schindler]

1+2. Let's do in in Martin's way.
3. Lets call it src/helpers
4. Let's split it in two examples. One of them is simpler than original and the second one demonstrates usage in MDN-like way, e.g. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/round

[mbohal]

@bedrich-schindler it is fixed I think. Please take a look.

[lukasbriza]

Add MDN-style documentation for the className function.