MonoGame 3.4 Content extension?

Hello,

I recently (like 1 hour ago) started to port one of my ooold XNA samples to MonoGame. For this I need a custom content pipeline extension but I have been stuck on this for a while now. Could you please point in me in the directions on how to create a content pipeline extension?

EDIT : Problem solved. If anyone wonders, the most straightforward way is to pull the MonoGame source and add the extension there. I found it easier to work directly in the monogame content processor.