Pattern generators

[RunDevelopment]

This is based on the idea of @LeaVerou (#1479 (comment))

We could also have factory helpers, e.g. Prism.keywords("foo", "bar", ...) that generate regexes for common things

The only difference is that Prism.keywords will not generate a regex but an array with a method/property generate. This method will be called when the pattern is used for the first time and returns a regex.
Like this, we can have lists of keywords which can be used and modified by other languages.

Thoughts?

[RunDevelopment]

The keywords function could then look like this:

function keywords(keywords, caseInsensitive) {
	keywords.generate = function (keywords) {
		return RegExp('\\b(?:' + keywords.join('|') + ')\\b', caseInsensitive ? 'i' : '');
	};
	return keywords;
}