WP Symposium - 5th pass update

* Adds support for converting `[youtube]`/`[/youtube]` BBCode
* Adds support for converting smileys to WordPress smileys
Fix reply forum callback

(We are reading a forum ID so don't try to convert a topic id to forum
id)
Merge pull request #4 from ntwb/master

WP Symposium - 5th pass update