Add new include_wolfram layer with wolfram output

[nicodjimenez]

The purpose is to provide a search string compatible with WolframAlpha computational engine (https://www.wolframalpha.com/). We can base this on our existing asciimath implementation. The ideal Wolfram output shown in these examples is basically almost identical to text + asciimath (with no delimiters).

Also note that we want to be able to build a single WolframAlpha search string from the whole MMD string. We can do this via

parseMarkdownByHTML(html)

which could emit type="wolfram_equation" for each sub equation (maybe this could be useful in Snip?), as well as one single type="wolfram" entry for the whole output (for search applications that want to leverage the W/A engine which is the main purpose here).

Note that tentative progress has been made in the mose/wolfram-support branch. Moses and I struggled a little with getting the dev setup working, perhaps some things can be updated to improve the dev experience.

[ykolodnitskiy]

Email kyle@learnwithjuni.com once released.