Add KaTeX support (#164)

* Add render-latex-using-katex.md to Demonstarate how to use the katex

* Update math.html add katex scripts and css

exampleSite/content/posts/render-latex-using-katex.md

@@ -0,0 +1,36 @@
++++
+date = "2019-03-20"
+title = "Render LaTeX using KaTeX"
+description = "Katex support demo"
+katex = "true"
+series = ["Theme", "Hugo"]
++++
+
+Enable katex by adding `katex = "true"` to the [front matter](https://gohugo.io/content-management/front-matter/)  
+
+```toml
++++
+katex = "true"
++++
+```
+
+It's almost a dropin alternative to the mathjax solution,you should just choose one of them.  
+
+Inline math looks like this  
+
+```tex
+This is text with inline math $\sum_{n=1}^{\infty} 2^{-n} = 1$
+```
+
+This is text with inline math $\sum_{n=1}^{\infty} 2^{-n} = 1$  
+and with math blocks:  
+
+```tex
+$$
+\sum_{n=1}^{\infty} 2^{-n} = 1
+$$
+```
+
+$$
+\sum_{n=1}^{\infty} 2^{-n} = 1
+$$

layouts/partials/posts/math.html

@@ -22,3 +22,17 @@
     });
   </script>
 {{- end -}}
+{{- if .Params.katex -}}
+  <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/katex@0.10.1/dist/katex.min.css" integrity="sha384-dbVIfZGuN1Yq7/1Ocstc1lUEm+AT+/rCkibIcC/OmWo5f0EA48Vf8CytHzGrSwbQ" crossorigin="anonymous">
+  <script defer src="https://cdn.jsdelivr.net/npm/katex@0.10.1/dist/katex.min.js" integrity="sha384-2BKqo+exmr9su6dir+qCw08N2ZKRucY4PrGQPPWU1A7FtlCGjmEGFqXCv5nyM5Ij" crossorigin="anonymous"></script>
+  <script defer src="https://cdn.jsdelivr.net/npm/katex@0.10.1/dist/contrib/auto-render.min.js" integrity="sha384-kWPLUVMOks5AQFrykwIup5lo0m3iMkkHrD0uJ4H5cjeGihAutqP0yW0J6dpFiVkI" crossorigin="anonymous"
+    onload="renderMathInElement(document.body,
+      {
+        delimiters: [
+          {left: '$$', right: '$$', display:true},
+          {left: '$', right: '$', display:false},
+        ]
+      }
+    );">
+  </script>
+{{- end -}}