fix(italicsAndBold): Make italicsAndBold lazy (#608)

fix italicsAndBold if literalMidwordUnderscores option is enabled
it should end at the nearest closing underscores, not the furthest

Closes #544

Author: VladimirV99

dist/showdown.js

@@ -8,11 +8,17 @@ showdown.subParser('underline', function (text, options, globals) {
   text = globals.converter._dispatch('underline.before', text, options, globals);
 
   if (options.literalMidWordUnderscores) {
-    text = text.replace(/\b_?__(\S[\s\S]*)___?\b/g, function (wm, txt) {
+    text = text.replace(/\b___(\S[\s\S]*?)___\b/g, function (wm, txt) {
+      return '<u>' + txt + '</u>';
+    });
+    text = text.replace(/\b__(\S[\s\S]*?)__\b/g, function (wm, txt) {
       return '<u>' + txt + '</u>';
     });
   } else {
-    text = text.replace(/_?__(\S[\s\S]*?)___?/g, function (wm, m) {
+    text = text.replace(/___(\S[\s\S]*?)___/g, function (wm, m) {
+      return (/\S$/.test(m)) ? '<u>' + m + '</u>' : wm;
+    });
+    text = text.replace(/__(\S[\s\S]*?)__/g, function (wm, m) {
       return (/\S$/.test(m)) ? '<u>' + m + '</u>' : wm;
     });
   }

dist/showdown.js.map

@@ -2,3 +2,4 @@
 <p><u>an underlined sentence</u></p>
 <p><u>three underscores are fine</u></p>
 <p>_single_ underscores are left alone</p>
+<p><u>multiple</u> underlines in a <u>paragraph</u></p>

dist/showdown.min.js

@@ -5,3 +5,5 @@ __an underlined sentence__
 ___three underscores are fine___
 
 _single_ underscores are left alone
+
+__multiple__ underlines in a __paragraph__