replace spaces with dashes in filenames

PLEASE DONT MERGE AS IS

Hi Zach, I'm a *very* happy paid up customer of PS Notes but I needed this quick hack to replace spaces with dashes for myself as that's the convention I use for my notes files. 

If you have time, it would be great if you could incorporate this as config option, though I know that's asking alot as I myself really like the clean simplicity you have with the app right now. Maybe even as a cmd line option so as not to burden the normal UI ?

I also added quick note to README on some extra deps required to compile that I didn't already have on my 12.04 install.