Fix for HTML Keyword highlighting.

The keyword highlighting in HTML code is broken if there are not attributes for a tag!

The following markdown code:

```html
<div>Test</div>


will create:

    
    <div>test</div>


which looks like this:

&lt;**div&gt;Test&lt;/div&gt;**

instead of:

    
    <div>test</div>



which looks like this:

&lt;**div**&gt;Test&lt;**/div**&gt;

This was pretty easy to fix by just adding the & (of &amp;gt;) as additional end besides of a space. I also changed the space to the /s regex so it also works in the (possible) case that a tag continues with a line break or a tab character.

rstacruz / flatdoc

Fix for HTML Keyword highlighting. #28