Markup: addInline improvements

[RunDevelopment]

I took a long hard look at addInline from #1660 and made some improvements.

• The new version doesn't use the rest property.
• The resulting token stream is flatter because content was removed.

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Btw.: With ES6 computed properties, the whole addInline function can be simplified to something which looks a whole lot more like a language definition:

function addInlined(tagName, lang) {
    Prism.languages.insertBefore('markup', 'cdata', {
        [tagName]: {
            pattern: RegExp(/(<__[\s\S]*?>)(?:<!\[CDATA\[[\s\S]*?\]\]>\s*|[\s\S])*?(?=<\/__>)/.source.replace(/__/g, tagName), 'i'),
            lookbehind: true,
            greedy: true,
            inside: {
                'included-cdata': {
                    pattern: /<!\[CDATA\[[\s\S]*?\]\]>/i,
                    inside: {
                        ['language-' + lang]: {
                            pattern: /(^<!\[CDATA\[)[\s\S]+?(?=\]\]>$)/i,
                            lookbehind: true,
                            inside: Prism.languages[lang]
                        },
                        'cdata': /^<!\[CDATA\[|\]\]>$/i
                    }
                },
                ['language-' + lang]: {
                    pattern: /[\s\S]+/,
                    inside: Prism.languages[lang]
                }
            }
        }
    });
}

So, #1578 when?