FEATURE: Update KaTeX renderer to v0.11.1 (#18)

Mostly bug fixes and couple new features.
This version is now live on khanacademy.org

public/katex/README.md

@@ -0,0 +1,32 @@
+
+## How to build KaTeX for Discourse
+
+1. `git clone https://github.com/KaTeX/KaTeX.git && cd KaTeX`
+
+    `git submodule update --init --recursive`
+
+2. Disable TTF fonts:
+
+   `export USE_TTF=false`
+
+3. Run build to fetch the fonts into `dist/fonts/`
+
+   `npm run build`
+
+4. Copy fonts to this plugin
+
+   `cp dist/fonts/* discourse-math/public/katex/fonts/`
+
+5. Change paths to fonts ((otherwise the fonts won't load in Discourse):
+
+    `sed -ri 's/@font-folder.+$/@font-folder:
+"\/plugins\/discourse-math\/katex\/fonts";/'
+submodules/katex-fonts/fonts.less`
+
+3. Build KaTeX:
+
+   `yarn && yarn builld`
+
+4. Copy `katex.min.js` and `katex.min.css` from `dist/` to
+`discourse-math/public/katex/`
+