Add better lint checking.

Summary:
Make the lint checker check more files. Also, make arc run the
linter.

Test Plan:
 - `arc lint`
 - `make lint`

Reviewers: kevinb, alpert

Reviewed By: alpert

Differential Revision: https://phabricator.khanacademy.org/D17509

test/katex-spec.js

@@ -1,3 +1,9 @@
+/* global beforeEach: false */
+/* global jasmine: false */
+/* global expect: false */
+/* global it: false */
+/* global describe: false */
+
 var buildHTML = require("../src/buildHTML");
 var buildMathML = require("../src/buildMathML");
 var katex = require("../katex");