Possible fix for huge code blocks (#142)

I'd like to propose a fix for issue #142, but unfortunately I don't have access to a local web server currently, so this has **NOT** been tested, and should be locally tested before merging.

The modified PHP code is supposed to remove excess `<br>` tags from the generated html of the bbcode tag. [I added it based on this documentation](http://nbbc.sourceforge.net/readme.php?page=usage_call)

Expected result of the fix:
![](http://i.imgur.com/XfDL5ac.png)