Don't run in Safari

Summary: Safari has weird bugs associated with inline-table and
vertical-align, so we just won't render in Safari.

Auditors: alpert

katex.js

@@ -244,6 +244,10 @@ var clearNode = function(node) {
 };
 
 var process = function(toParse, baseNode) {
+    if (utils.isSafari) {
+        throw new ParseError("KaTeX doesn't work on Safari");
+    }
+
     clearNode(baseNode);
     var tree = parseTree(toParse);
 

utils.js

@@ -13,6 +13,17 @@ function slowContains(list, elem) {
 
 var contains = Array.prototype.indexOf ? fastContains : slowContains;
 
+function isSafari() {
+    var userAgent = navigator.userAgent.toLowerCase();
+
+    // Steal these regexes from jQuery migrate for browser detection
+    var webkit = /(webkit)[ \/]([\w.]+)/.exec(userAgent);
+    var chrome = /(chrome)[ \/]([\w.]+)/.exec(userAgent);
+
+    return webkit && !chrome;
+}
+
 module.exports = {
-    contains: contains
+    contains: contains,
+    isSafari: isSafari()
 };