Filter should understand complex styles

[Piotrek Koszuliński]

Currently it won't create rules from following styles:

font_style: {
	element: 'span',
	attributes: { 'class': '#(family)' },
	overrides: [
		{
			element: 'span',
			attributes: {
				'class': /^Font(?:Comic|Courier|Times)$/
			}
		}
	]
},

fontSize_sizes: 'Smaller/FontSmaller;Larger/FontLarger;8pt/FontSmall;14pt/FontBig;Double Size/FontDouble',
fontSize_style: {
	element: 'span',
	attributes: { 'class': '#(size)' },
	overrides: [
		{
			element: 'span',
			attributes: {
				'class': /^Font(?:Smaller|Larger|Small|Big|Double)$/
			}
		}
	]
}

Perhaps this can be a part of #9991.