Export logic for determining whether the prompt should be shown

[Mesoptier]

If this logic is exported, developers can implement code-splitting for this component and thus avoid loading any additional data (the prompt, icons, and styles) unless it is actually needed.

For example:

import React, { Suspense } from 'react';
import { shouldShowPrompt } from 'react-ios-pwa-prompt';

const LazyPWAPrompt = React.lazy(() => import('react-ios-pwa-prompt'));

function App() {
    const options = {
        timesToShow: 1,
        promptOnVisit: 2,
    };

    return (
        <>
            {shouldShowPrompt(options) && (
                <Suspense fallback={null}>
                    <LazyPWAPrompt {...options} />
                </Suspense>
            )}
        </>
    );
}

@chrisdancee If this sounds like a good idea, I'll open a PR!

[chrisdancee]

Sounds like a great idea!
Feel free to drop a PR and I'll get straight onto reviewing it :)