Allow markdown ```example to render interactive example.

[uipoet]

Markdown fenced code blocks without a syntax prevent text editors from enabling syntax features within the code block.

This change allows fenced code blocks with jsx syntax to render the same as without a syntax specified.

[mik01aj]

If you change this, then you should update the docs too. See: https://github.com/sapegin/react-styleguidist/search?utf8=%E2%9C%93&q=fenced

[sapegin]

Then how would we make a JSX code example that shouldn’t be rendered as a playground?

[uipoet]

@mik01aj Thanks, I will update relevant docs.

@sapegin How about a unique fence type that won't conflict? We can configure our editors to treat any fence type as an alias to a valid one. I suggest example or playground.

[sapegin]

example is fine, thanks!