Support Cancellation of Terms in MathML

[NV-Codes]

Description

It would be very useful for Pandoc to be able to convert the \cancel, \bcancel, and \xcancel LaTeX commands to MathML as described below (from NSoiffer/MathCAT#341):

The way I would suggest is to use menclose . It has the attribute notation with many options. For cancellation, one or both values updiagonalstrike downdiagonalstrike would make sense.

<math>
   <menclose notation='downdiagonalstrike'>  <mfrac><mn>3</mn><mn>2</mn></mfrac> </menclose>
</math>

It currently seems that, when typing math in Pandoc's Markdown, base LaTeX and amsmath commands are able to be converted to MathML. The three commands listed above are part of the cancel package.