ELPA submission: mathjax.el

[Augusto Stoffel]

I would like to add the package residing at the following location to
ELPA:

https://github.com/astoff/mathjax.el

There's no need to clarify the necessary header changes, but I would
like to add a technical comment: the package needs an external program
to be useful (Node) but otherwise bundles all other dependencies.

[paste Chico Buarque meme here]

More specifically, there's a 2.3 MB minified JavaScript file that is
committed to the repo and I will take care to update when the "real"
source (also in the repo, of course) changes.

Also, in case there are any JS experts around, I'd be happy to get hints
on how to make things work with other JS engines.  I have at least 3
others in my machine (2 browsers and Gnome's) but it's unclear to me if
they can be used for random purposes like this one.

Best,
Augusto