Support XFT multiple fonts

Hi there, I incorporated @csstaub's modifications in his csstaub/X11-xft to support multiple XFT fonts in xmobar.

It works like this:
![2014-09-17-142101_2560x1600_scrot](https://cloud.githubusercontent.com/assets/635957/4299309/2f6f0da6-3e34-11e4-82fa-fe2605cf7b08.png)