Anamorph output

[skinkie]

First of all: very great library. After https://github.com/chinasaur/poptart I find this one of the most useful pieces of code I found to use a raspberry pi in broadcasting. Something 'nice' with vgfont would be still appreciated. But I do have another request.

We currently use anamorph output. Which means over HDMI we use 720x576, hdmi_group=1, hdmi_mode=22. Virtually all tools including raspidmx when displaying pictures will shrink the picture, opposed to display it in the correct aspect ratio. What can be done to solve this at the core of the library?