Add basic auto-render extension

Summary:
Add an auto-render extension to render math on a page. It
exposes a global function (maybe we should attach it to `katex`?) to
render math in an element. It comes with a README on how to use it.
Also, make `make build` build the minified file.

Fixes #26

Test Plan:
 - Visit http://localhost:7936/contrib/auto-render/
 - See that all of the math renders correctly
 - `make test`

Reviewers: alpert, kevinb

Reviewed By: kevinb

Differential Revision: https://phabricator.khanacademy.org/D16620

package.json

@@ -17,7 +17,7 @@
     "browserify": "~2.29.1",
     "clean-css": "~2.2.15",
     "express": "~3.3.3",
-    "jasmine-node": "git://github.com/mhevery/jasmine-node.git#Jasmine2.0",
+    "jasmine-node": "2.0.0-beta4",
     "jshint": "^2.5.6",
     "less": "~1.7.5",
     "uglify-js": "~2.4.15"