Support ECMAScript imports in examples

[sapegin]

It shouldn't be hard to support the most common import variations in the examples:

import Pizza from 'pizza';
import { Pizza as Falafel, Coffee } from 'lunch';
import Lunch, { Pizza as Falafel, Coffee } from 'lunch';

There are two places where we need to add this:

1. In styleguide-loader:

react-styleguidist/loaders/examples-loader.js

Line 40 in b66bd10

const requiresFromExamples = getRequires(codeFromAllExamples);

We may want to use something like detect-import-require instead of a custom RegExp.

2. On the frontend:

react-styleguidist/src/rsg-components/ReactExample/ReactExample.js

Lines 66 to 76 in b66bd10

	compileCode(code) {
	try {
	const wrappedCode = code.trim().match(/^</) ? wrapCodeInFragment(code) : code;
	return compileCode(wrappedCode, this.props.compilerConfig);
	} catch (err) {
	if (this.props.onError) {
	this.props.onError(err);
	}
	}
	return false;
	}

rewrite-imports may be a good start, but it doesn't support multiline statements.