Add simple CLI

cli.js

@@ -0,0 +1,15 @@
+#!/usr/bin/env node
+// Simple CLI for KaTeX.
+// Reads TeX from stdin, outputs HTML to stdout.
+
+var katex = require("./");
+var input = "";
+
+process.stdin.on("data", function(chunk) {
+  input += chunk.toString();
+});
+
+process.stdin.on("end", function() {
+  var output = katex.renderToString(input);
+  console.log(output);
+});