It's just a short javascript file. I just cat the text through a ssh connection into this [script](http://tmp.fnordig.de/post.js). It parses the content using [markdown-js](https://github.com/evilstreak/markdown-js) and re-writes the index.html file.
This way I can write a post wherever I have ssh access to my server (and as I've got a smartphone, that's nearly everywhere).