feat: Support mtable, mtd, mtr for draw matrix.

[fukatani]

I want mtable, mtr and mtd for drawing matrix.

testcase:

  <math xmlns='http://www.w3.org/1998/Math/MathML'>
    <mtable>
      <mtr>
        <mtd>
          <mi>x</mi>
        </mtd>
        <mtd>
          <mn>3</mn>
        </mtd>
      </mtr>
      <mtr>
        <mtd>
          <mrow>
            <mo>-</mo>
            <mn>1</mn>
          </mrow>
        </mtd>
        <mtd>
          <mi>y</mi>
        </mtd>
      </mtr>
    </mtable>
  </math>