Fix GH-281 extra blank lines in output

src/ReverseMarkdown.Test/ConverterTests.WhenListContainsMultipleParagraphs_ConvertToMarkdownAndIndentSiblings.verified.md

@@ -1,8 +1,6 @@
 1. Paragraph 1
 
-        
     Paragraph 1.1
 
-        
     Paragraph 1.2
 2. Paragraph 3

src/ReverseMarkdown.Test/ConverterTests.WhenThereIsEmptyBlockquoteTag_ThenConvertToMarkdownBlockquote.verified.md

@@ -1,4 +1,3 @@
 This text has 
 
-
 . This text appear after header.

src/ReverseMarkdown.Test/ConverterTests.WhenThereIsEmptyPreTag_ThenConvertToMarkdownPre.verified.md

@@ -1,5 +1,3 @@
 This text has pre tag content 
 
-
-
 Next line of text

src/ReverseMarkdown.Test/ConverterTests.WhenThereIsEmptyPreTag_ThenConvertToMarkdownPre_GFM.verified.md

@@ -1,4 +1,4 @@
-This text has pre tag content 
+This text has pre tag content 
 
 ```
 

src/ReverseMarkdown/Converter.cs

@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.Linq;
 using System.Reflection;
+using System.Text.RegularExpressions;
 using HtmlAgilityPack;
 using ReverseMarkdown.Converters;
 
@@ -56,6 +57,9 @@ public string Convert(string html)
 
             var result = Lookup(root.Name).Convert(root);
 
+            // cleanup multiple new lines
+            result = Regex.Replace( result, @"(^\p{Zs}*(\r\n|\n)){2,}", Environment.NewLine, RegexOptions.Multiline);
+
             return result.Trim();
         }