I've written a new library to convert AsciiMath to TeX: https://github.com/christianp/asciimath2tex

There's an 'official' asciimath to tex JS file at https://github.com/asciimath/asciimathml/blob/master/asciimath-based/ASCIIMathTeXImg.js but it doesn't seem to do matrices, and is written in v old JS.

This is to use with a customised StackEdit for a student with reduced mobility, so we prefer AsciiMath to TeX.

StackEdit uses KaTeX for its maths rendering, so I couldn't render MathML.