Add ability to utilize Markdown on Save in other plugins

[jchristopher]

I'm currently working on a variant of Press This! to allow for rapid linkblogging, and I'd love to be able to use Markdown on Save when writing the post content. As it stands there's no way for me to create a post programmatically and have Markdown on Save's actions/filters run, but I'd love for that to happen! Thanks for such an awesome plugin, Mark!