Added support for KaTeX rendering using markdown-it-katex

[erobl]

Solves issue #15 with KaTeX rendering. I figured it's lightweight enough to leave as a default option, but I can also hide it behind a flag if it's necessary.

[shime]

Looks good to me. Maybe we could include this - what are your thoughts, @niftylettuce?

[rcgalbo]

What is the status of this? Would be very useful for my markdown documents!

[erobl]

I've been using it for a while on my own build, and there's some bugs with the rendering. I can't find what's wrong with it.

[shime]

@erobl what kind of bugs? Did you report it to markdown-it-katex maintainers?

[erobl]

No, the main problem is that I'm not sure if I'm missing a font or a style, perhaps the style that's included in the project is conflicting with the spacing on the equations? Multiline equations aren't rendering properly:

The equations render fine on their demo, so it's probably my fault.

Edit:
It seems to be related with this issue. I downgraded the KaTeX CSS and it's working now. I'll be uploading the new commit soon.

[samkimhis]

The commits by @erobl work beautifully on my system (macOS, vim) for rendering equations and appear to be much faster than the MathJax workaround (instant-markdown/vim-instant-markdown#67). Could you close this pull request? I think a lot of people will benefit from this feature.

[sulibo]

It will be nice if this pull request can be merged.

[ysftaha]

Is @shime dead?

[hcgatewood]

Xpost from another thread: Until this gets resolved/pulled, feel free to check out my fork which includes automatic handling of KaTeX equations @hcgatewood/livedown. Installation via npm install -g git+https://github.com/hcgatewood/livedown.