Improve testing

Summary:
Move dom creation into katex.js so our tests can test non-dom things, and add
some buildTree tests. Add some checks make utils.js work in node. Add support
for jasmine-node, to allow for command line unit testing.

Test Plan:
- Make sure tests work, in both the browser and with `make test`
- Make sure huxley screenshots didn't change

Reviewers: alpert

Reviewed By: alpert

Differential Revision: http://phabricator.khanacademy.org/D13125

katex.js

@@ -8,7 +8,7 @@ var process = function(toParse, baseNode) {
     utils.clearNode(baseNode);
 
     var tree = parseTree(toParse);
-    var node = buildTree(tree);
+    var node = buildTree(tree).toDOM();
 
     baseNode.appendChild(node);
 };