Add Greek letters

Summary: Fixes T1190.

Test Plan: `\alpha \beta \gamma \delta \epsilon \varepsilon \zeta \eta \theta \vartheta \iota \kappa \lambda \mu \nu \xi \omicron \pi \varpi \rho \varrho \sigma \varsigma \tau \upsilon \phi \varphi \chi \psi \omega \Gamma \Delta \Theta \Lambda \Xi \Pi \Sigma \Upsilon \Phi \Psi \Omega`

Reviewers: emily

Reviewed By: emily

Maniphest Tasks: T1190

Differential Revision: http://phabricator.khanacademy.org/D3054

katex.js

@@ -172,7 +172,49 @@ var charLookup = {
     "\\rvert": "|",
     "\\space": "\u00a0",
     "\\times": "\u00d7",
-    "\\to": "\u2192"
+    "\\to": "\u2192",
+
+    "\\alpha": "\u03b1",
+    "\\beta": "\u03b2",
+    "\\gamma": "\u03b3",
+    "\\delta": "\u03b4",
+    "\\epsilon": "\u03f5",
+    "\\zeta": "\u03b6",
+    "\\eta": "\u03b7",
+    "\\theta": "\u03b8",
+    "\\iota": "\u03b9",
+    "\\kappa": "\u03ba",
+    "\\lambda": "\u03bb",
+    "\\mu": "\u03bc",
+    "\\nu": "\u03bd",
+    "\\xi": "\u03be",
+    "\\omicron": "\u03bf",
+    "\\pi": "\u03c0",
+    "\\rho": "\u03c1",
+    "\\sigma": "\u03c3",
+    "\\tau": "\u03c4",
+    "\\upsilon": "\u03c5",
+    "\\phi": "\u03d5",
+    "\\chi": "\u03c7",
+    "\\psi": "\u03c8",
+    "\\omega": "\u03c9",
+    "\\varepsilon": "\u03b5",
+    "\\vartheta": "\u03d1",
+    "\\varpi": "\u03d6",
+    "\\varrho": "\u03f1",
+    "\\varsigma": "\u03c2",
+    "\\varphi": "\u03c6",
+    "\\Gamma": "\u0393",
+    "\\Delta": "\u0394",
+    "\\Theta": "\u0398",
+    "\\Lambda": "\u039b",
+    "\\Xi": "\u039e",
+    "\\Pi": "\u03a0",
+    "\\Sigma": "\u03a3",
+    "\\Upsilon": "\u03a5",
+    "\\Phi": "\u03a6",
+    "\\Psi": "\u03a8",
+    "\\Omega": "\u03a9"
 };
 
 var textit = function(value) {