Refactor
Declare domain static so that functions (including load_prettify, get_option, pre_textarea_prettify etc) can be declared static. This makes these methods readily available outside the class. (The class is effectively a singleton, so probably should just follow that pattern).
Ensure the toolbar javascript runs as late as possible. Fixes conflict with Shortcoder which calls Qtags late on and destroys the markdown toolbar. Fixes #53.