Don't use regex that can be slow

lib/inlines.js

@@ -984,13 +984,33 @@ var parseInlines = function(block) {
     // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/trim#return_value
     // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Lexical_grammar#white_space
     // Removes only ASCII tab and space.
-    this.subject = block._string_content.replace(/^[\t \r\n]+|[\t \r\n]+$/g, "")
+    this.subject = trim(block._string_content)
     this.pos = 0;
     this.delimiters = null;
     this.brackets = null;
     while (this.parseInline(block)) {}
     block._string_content = null; // allow raw string to be garbage collected
     this.processEmphasis(null);
+
+    function trim(str) {
+        let start = 0;
+        for(; start < str.length; start++) {
+            if (!isSpace(str[start])) {
+                break;
+            }
+        }
+        let end = str.length - 1;
+        for(; end >= start; end--) {
+            if (!isSpace(str[end])) {
+                break;
+            }
+        }
+        return str.slice(start, end + 1);
+
+        function isSpace(c) {
+            return c === " " || c === "\t" || c === "\n" || c === "\r";
+        }
+    }
 };
 
 // The InlineParser object.