Refactor to improve performance of email regex

Closes GH-8.
Related-to: GH-9.

Author: wooorm

lib/index.js

@@ -132,7 +132,7 @@ function transformGfmAutolinkLiterals(tree) {
     tree,
     [
       [/(https?:\/\/|www(?=\.))([-.\w]+)([^ \t\r\n]*)/gi, findUrl],
-      [/([-.\w+]+)@([-\w]+(?:\.[-\w]+)+)/g, findEmail]
+      [/(?<=^|\s|\p{P}|\p{S})([-.\w+]+)@([-\w]+(?:\.[-\w]+)+)/gu, findEmail]
     ],
     {ignore: ['link', 'linkReference']}
   )
@@ -274,6 +274,7 @@ function previous(match, email) {
     (match.index === 0 ||
       unicodeWhitespace(code) ||
       unicodePunctuation(code)) &&
+    // If it’s an email, the previous character should not be a slash.
     (!email || code !== 47)
   )
 }