Pre-RFC: Rustdoc LaTeX-style math

I generally support the idea of enabling people to write math in rustdoc, and the choice of LaTeX-style math notation backed by katex.

I want to request something of the implementation : Please make sure that the math source code is converted to MathML at render time, and therefore degrades gracefully if katex's JavaScript and/or CSS fail to load. (Last I checked, katex could do this, but it wasn't its default mode.)