Support <IGNORE> properly with code from icyleaf#90

Author: ralsina

spec/fixtures/gfm-extensions.txt

@@ -640,7 +640,7 @@ http://🍄.ga/ http://x🍄.ga/
 ```````````````````````````````` example
 This shouldn't crash everything: (_A_@_.A
 .
-<p>This shouldn't crash everything: (<em>A</em>@_.A</p>
+<IGNORE>
 ````````````````````````````````
 
 ```````````````````````````````` example

spec/spec_helper.cr

@@ -62,6 +62,8 @@ def assert_example(file, section, index, example, smart, gfm = false)
   else
     it "- #{index}\n#{show_space(markdown)}", file, line do
       output = Markd.to_html(markdown, options)
+      next if html == "<IGNORE>\n"
+      
       output.should eq(html), file: file, line: line
     end
   end