Add "tokenDelimeter" option (because single curlies conflict with JS blocks)

[pzhine]

Current behavior

const template = `
<meta name="description" content="{META_DESCRIPTION}">
<script>
    window.dataLayer = window.dataLayer || [];
    function gtag(){dataLayer.push(arguments);}
    gtag('js', new Date());
    gtag('config', 'UA-112910279-1');
</script>
`
const tokens = { META_DESCRIPTION: 'This is a website about dogs' }
const rendered = renderTemplate(template, tokens)

rendrered would then be:

<meta name="description" content="This is a website about dogs">
<script>
    window.dataLayer = window.dataLayer || [];
    function gtag()undefined
    gtag('js', new Date());
    gtag('config', 'UA-112910279-1');
</script>

Note: undefined where function block should be is undesirable.

Desired behavior

Add an options parameter with a single option key: tokenDelimeter. Possible values are module constants SINGLE_CURLY (default) and DOUBLE_CURYLY.
Then we can do this:

import renderTemplate, { DOUBLE_CURLY } from 'react-text-templates'
const template = `
<meta name="description" content="{{META_DESCRIPTION}}">
<script>
    window.dataLayer = window.dataLayer || [];
    function gtag(){dataLayer.push(arguments);}
    gtag('js', new Date());
    gtag('config', 'UA-112910279-1');
</script>
`
const tokens = { META_DESCRIPTION: 'This is a website about dogs' }
const rendered = renderTemplate(template, tokens, { tokenDelimiter: DOUBLE_CURLY })