There is a way to do it and I'm successfully using it in Yosemite. It's called MenuAndDockless which requires something called "Simbl" to be installed. My menu "autohides" which recovers extra screen space and animates back in when I hold my mouse at the top of the screen. It's exactly what I've been looking for. You can set it to hide the menu on a per app basis although it seems older apps will not work.