Fix highlighting xml/html code by escaping html characters

[anton-sergeev]

Here is bug, no escape html characters:

After fix:

[anton-sergeev]

This related to #18, #21, #26 Issues

[miloja]

This is not a proper fix. You should check file extension and language given

[anton-sergeev]

This is a common problem for html-like tags inside any language preformatted text. For example if I post the next:

<pre><code class="ruby">
some_string = "start <b>ddd</b>"
</code></pre>

I got the next result:

And with escaping suggested in this pull request:

[miloja]

You're right. The fix is very ok. I haven't thought about HTML hidden in ruby string constant. :)