Add support for Pandoc tex_math_single_backslash syntax extension

[Witiko]

We should add support for Pandoc tex_math_single_backslash syntax extension.
Progresses #61.

Assigned to @lostenderman as part of grant project MUNI/33/1658/2022.
Tentatively scheduled for milestone 2.22.0 to be delivered by March 31, 2023.

[lostenderman]

Would this be a good way to define renderers for the different tex math extensions?

• tex_math_dollars

\def\markdownRendererDollarsInlineMathPrototype#1{%
  \markdownRendererInlineMath{#1}}%
\def\markdownRendererDollarsDisplayMathPrototype#1{%
  \markdownRendererDisplayMath{#1}}%

• tex_math_single_backslash

\def\markdownRendererSingleBackslashInlineMathPrototype#1{%
  \markdownRendererInlineMath{#1}}%
\def\markdownRendererSingleBackslashDisplayMathPrototype#1{%
  \markdownRendererDisplayMath{#1}}%

• tex_math_double_backslash

\def\markdownRendererDoubleBackslashInlineMathPrototype#1{%
  \markdownRendererInlineMath{#1}}%
\def\markdownRendererDoubleBackslashDisplayMathPrototype#1{%
  \markdownRendererDisplayMath{#1}}%

• these would defined as they are now

\def\markdownRendererInlineMathPrototype{...}
\def\markdownRendererDisplayMathPrototype{...}

Each would have its pair of renderers for inline and display math which
would be rendered via a shared pair of renderers, so each one could be redefined separately
but also all tex inline or display math could be redefined at once.

[Witiko]

I would be in favor of having just a single pair of renderers. Each renderer should correspond to a semantic element. It does not seem to me that the elements given by the different syntax extensions for math consistute independent semantic elements.