Merge pull request #3 from jrfnl/master

Lower priority for our content filter to ensure that shortcodes are resolved before our filter is run.
new features / enhancements and a small bug fix

* [New feature] Added extensibility to classnames and filetypes,
meaning that users can add a filter hook to edit/add their own styles
* [New feature] Added debug mode to async replacement
* [Bug fix] async replacement was balking at <a name> nodes
whoops. Bad find and replace, bad
[Bug fix] settings links on plugin page didn't work, thanks [sndu for reporting](http://wordpress.org/support/topic/500-server-error-on-settings-icons-not-displaying)