[HACKTOBERFEST] Add MathML

[kboshold]

It should be possible to print mathml. When rendering the following HTML:

<div>
	<math xmlns="http://www.w3.org/1998/Math/MathML">
		<mn>7</mn>
		<mfrac>
			<mrow>
				<mi>x</mi>
				<mo>+</mo>
				<mi>y</mi>
			</mrow>
			<mrow>
				<mo>π</mo>
				<mn> </mn>
				<mo>*</mo>
				<mn>4</mn>
				<mn>2</mn>
				<mn> </mn>
			</mrow>
		</mfrac>
	</math>
</div>

the following formula should be rendered into the document:

This should, of course, also be included in the tests.